The genus Haeckeliana comprises the spherical Circoporida, with dimpled, porcellanous shell, which are widely distributed, but rather rare, in depths between 2000 and 3000 fathoms. All the known species (six in number) are very closely related, and though the extreme forms appear very different in size and structure, they are so connected by a continuous series of intermediate forms, that they may be regarded as varieties of a single species, first observed by Dr. John Murray, and called by him Haeckeliana porcellana. The number of radial spines may be from sixteen to fifty-five, and is usually between thirty and forty. Each is surrounded by a basal coronet of aspinal pores, usually five, more rarely four or six; the number, however, is not constant in any one species. Each coronet is armed with an outer ring of by-spines. The surface of the shell between the coronets is dimpled. The mouth (Pl. 114, fig. 3) is about as large as a corona, and also armed with a ring of by-spines. The structure of the thick porcellanous shell and the radial spines is different from the other Circoporida.

1. Haeckeliana porcellana, John Murray (Pl. 114, fig. 6).

Shell with forty to forty-five coronets, the majority of which have five pores (more rarely four or six). Coronets broader than their intervals, and twice as broad as the length of the by-spines. Dimples subcircular, of the same breadth as the pores. Main-spines about as long as the radius.

Dimensions.—Diameter of the shell 0.37 to 0.42, of the coronets 0.06 to 0.07.

Habitat.—South Pacific, Stations 289 to 293, depth 2025 to 2550 fathoms.

2. Haeckeliana maxima, n. sp. (Pl. 114, fig. 5).

Shell with fifty to fifty-five coronets, the majority of which have six pores (more rarely five or seven). Coronets broader than their intervals, and eight to ten times as broad as the length of the by-spines. Dimples irregularly polygonal, of about the same breadth as the pores. Radial main-spines about as long as the diameter of the shell.

Dimensions.—Diameter of the shell 0.5 to 0.52, of the coronets 0.08 to 0.09.

Habitat.—Equatorial Atlantic, Station 347, depth 2250 fathoms.

3. Haeckeliana lamarckiana, n. sp. (Pl. 114, fig. 4).

Shell with thirty-five to forty coronets, the majority of which have five pores (more rarely six or four). Coronets broader than their intervals; each funnel-shaped pore on the inside with a circle of small conical thorns. By-spines rudimentary or wanting. Dimples irregularly polygonal, half as broad as the pores. Radial main-spines shorter than the radius.

Dimensions.—Diameter of the shell 0.38 to 0.45, of the coronets 0.06 to 0.07.

Habitat.—South Atlantic, Stations 318 to 333, depth 2000 to 2900 fathoms.

4. Haeckeliana murrayana, Haeckel.

Shell with twenty to twenty-five coronets, the majority of which have five pores (more rarely four or six). Coronets of about the same breadth as their intervals, and twice as broad as the by-spines. Dimples subcircular, of about the same breadth as the pores. Radial main-spines about as long as the radius.

Dimensions.—Diameter of the shell 0.35 to 0.4, of the coronets 0.06 to 0.07.

Habitat.—Central Pacific, Stations 271 to 274, depth 2350 to 2750 fathoms.

5. Haeckeliana goetheana, n. sp. (Pl. 114, fig. 3).

Shell with sixteen to twenty coronets, the majority of which have four pores (more rarely five and very rarely six). Coronets smaller than their intervals. By-spines very short or rudimentary. Dimples subcircular, half as broad as the pores. Radial main-spines shorter than the radius.

Dimensions.—Diameter of the shell 0.25 to 0.3, of the coronets 0.04 to 0.05.

Habitat.—North Pacific (south of Japan), Station 231, depth 2250 fathoms.

6. Haeckeliana darwiniana, n. sp. (Pl. 114, figs. 1, 2).

Shell with twenty-six to thirty-two coronets, the majority of which have five pores (rarely four or six). Coronets smaller than their intervals and than the length of the by-spines. Dimples subcircular, half as broad as the pores, Radial main-spines longer than the radius.

Dimensions.—Diameter of the shell 0.30 to 0.42, of the coronets 0.07 to 0.08.

Habitat.—North Pacific (east of Japan), Stations 241 to 245, depth 2300 to 2900 fathoms.

Family LXXXII. Tuscarorida, n. fam. (Pl. 100).

Definition.—Phæodaria with an ovate, spindle-shaped, or nearly spherical shell exhibiting a peculiar solid porcellanous structure; with a few radial pores around the base of the hollow tubules, which are symmetrically arranged around the main axis and the mouth. Surface of the shell smooth or spiny, not tabulate nor panelled. Central capsule excentric, placed in the aboral half of the shell-cavity.

The Tuscarorida, and the preceding closely allied family, the Circoporida, represent together a peculiar small group, which differs from the other Phæodaria in the singular porcellanous structure of the shell-wall, and may be called Phæocalpia; their hollow radial spines are distinguished by peculiar basal pores, forming a circle around their base. The shell of the Tuscarorida is monaxonian, ovate, spindle-shaped or nearly spherical, whilst in the Circoporida it is polyaxonian, spherical or polyhedral; the hollow radial spines are arranged in the former around the main axis, in the latter around the common central point. All Phæocalpia (the Tuscarorida as well as the Circoporida) are inhabitants of great depths, usually between 2000 and 3000 fathoms.

Though the number of Tuscarorida at present known is small (only three genera, with ten species), they represent a very distinct and remarkable family of Phæodaria, as well by their considerable size, as by the peculiar arrangement of the radial spines and the structure of the shell-wall, which in some species is more solid and thicker than in any other Radiolaria. The diameter of the shell is always more than 1 mm., usually between 1 and 2, and sometimes more than 3 mm.

The dry shell of the Tuscarorida is not hyaline and transparent as is usual in the other Radiolaria, but perfectly opaque, milk-white or yellowish-white. This opacity is caused by innumerable very fine pores, which everywhere pierce the thick, apparently solid, fundamental substance of the shell-wall. Besides those very small pores, it is also pierced by a certain number of larger pores, which are scattered at wide distances (Narr. Chall. Exp., vol. i. pl. A, fig. 15b). These larger pores or pore-channels have a diameter of about 0.01 mm., and pierce the shell-wall either in a perpendicular or in an oblique direction. Very numerous straight, simple, and thin needles, usually 0.1 to 0.2 mm. in length, similar to the thin tangential needles of the Aulacanthida, are everywhere scattered tangentially in the cement-like fundamental substance, which seems to be a peculiar carbonic silicate; their axis is parallel to the shell-surface.

The general form of the shell is somewhat different in the three genera of Tuscarorida; ovate or spherical in Tuscarora and Tuscarusa, which bear no caudal axial spine (Pl. 100, figs. 1-7), or sometimes three-sided pyramidal (fig. 4); it is spindle-shaped in Tuscaridium, which bears on the aboral pore an axial caudal spine (Pl. 100, fig. 8). In every case the main axis of the shell, determining its monaxonian fundamental form, is indicated by the mouth, which is placed in the oral pole of the main axis and prolonged into a short tube or proboscis.

The hollow apophyses, arising from the shell of the Tuscarorida, are always cylindrical, long and thin tubules, the narrow cavity of which communicates directly with the large shell-cavity. In the axis of the tubules lies a thin axial chord or funicle, composed of a few (usually three or four) siliceous threads which arise from bridges between the basal pores of the apophyses, and are twisted together like the strands of a rope. The axial funicle is connected with the thin wall of the tubular apophyses by innumerable very thin radial beams, perpendicular to the axis (Pl. 100, fig. 3a, 5b). The surface of the apophyses is almost constantly covered with numerous small bristles or spines, which are usually curved and directed towards their distal ends.

Tuscarora (Pl. 100, figs. 1-6) exhibits two different groups of apophyses, which may be distinguished according to their different position and direction as "circoral teeth" and "aboral feet"; the teeth immediately surround the opening of the mouth, whilst the feet are remote from it and usually placed in the aboral half of the body, more rarely in the equator or in the oral half. The general form and structure are the same in both groups of apophyses, but their position and direction is different; the circoral teeth are directed forwards, often parallel (at the base at least), while the aboral feet are either divergent and directed backwards, or they diverge forwards in the basal part, then form a large arch, and finally curve backwards.

The number of the aboral feet, and their position relative to the circoral teeth, are different but probably constant in each single species, and serve, in the first place, for the distinction of genera and species. Tuscarora (in restricted sense) (Pl. 100, figs. 1-6), has constantly three feet (comparable to the three cortinar feet of the tripodal Nassellaria); Tuscarusa (Pl. 100, fig. 7) has four feet, opposite in pairs and forming a regular cross; Tuscaridium, finally (Pl. 100, fig. 8), has only one foot, which is situated in the main axis, on its aboral pole, and may therefore be called a caudal spine.

The number of the circoral teeth varies from two to four, and is usually three. Originally these three teeth alternate regularly with the three aboral feet, so that the latter may be regarded as perradial, the former as interradial (Pl. 100, figs. 1-4). The proportion of the number of each group of apophyses in the different species is synoptically shown in the following table:—

The base of the apophyses in all Tuscarorida is inflated, conical, and pierced by a small number of large ovate pores, the typical "basal pores," which occur also in the closely allied Circoporida. The number of these basal pores varies from two to eight, and is usually three or four; it never becomes in this family so great as in the Circoporida, where each circle of pores is often composed of sixteen to twenty-four or more basal pores. The number seems to be rather constant in each single species, as may be seen in the preceding Table. The pedal pores (on the base of the aboral feet) are usually larger than the dental pores (on the base of the circoral teeth). Their form is usually irregularly ovate or triangular; their outer aperture is armed with spines or bristles, which are commonly larger than in the other parts of the apophyses.

The mouth of the shell varies in form, according to the number and arrangement of the teeth on its corners. It is therefore a narrow transverse fissure, with two broad opposite lips and two corners, in the bidental forms (Pl. 100, figs. 5, 7), triangular in the tridental species (figs. 1-4), quadrangular or square in the quadridental species, Tuscarora belknapii (Narr. Chall. Exp., loc. cit., pl. A, fig. 15). The singular genus Tuscaridium (fig. 8) exhibits four teeth, which are nearly horizontally divergent in two pairs, a dorsal and a ventral pair (corresponding in position to the four feet of Tuscarusa, fig. 7); the mouth is here prolonged into a cylindrical, spinulate proboscis, which is curved towards the ventral face of the shell (fig. 8).

The central capsule of the Tuscarorida is kidney-shaped or spheroidal, scarcely half as large as the dark olive-green phæodium, which surrounds its anterior (oral) face. Usually the capsule and the phæodium together fill up the aboral half of the shell-cavity, and are separated from its walls by the calymma. The latter is pierced by numerous branched and reticulately anastomosing pseudopodia, which arise from the matrix enveloping the capsule, and pass over into a thin layer of sarcode, adjacent to the inner surface of the shell. The astropyle or the main-opening of the central capsule exhibits the usual radiate operculum and tubular proboscis of the Phæodaria (Pl. 115, fig. 3), and is directed towards the mouth of the shell. The number of the parapylæ or accessory openings seems to be variable in this family, and to correspond to the number of radial feet which arise from the shell. Therefore Tuscaridium possesses only one parapyle, which is diametrically opposite to the mouth, lies on the aboral pole of the capsule, and is directed towards the single caudal tube. Tuscarora seems to have three parapylæ, corresponding to the three radial feet, and Tuscarusa probably has four parapylæ, directed towards its four radial feet; in the latter genus, however, the capsule was not observed (the shell being empty); and in the other Tuscarorida this important and difficult anatomical question must be solved by further accurate examinations.

The nucleus is nearly half as large as the central capsule, ellipsoidal, and contains numerous nucleoli. In one specimen of Tuscarora belknapii I observed two nuclei in the central capsule, and in another specimen of the same species John Murray observed two central capsules (figured by him in the Narr. Chall. Exp., vol i. pl. A, fig. 15).

Synopsis of the Genera of Tuscarorida.

Genus 717. Tuscarora,^[333] John Murray, 1876, in schedulis, Chall. Coll.

Definition.—Tuscarorida with three radial aboral feet, and a variable number of circoral teeth.

The genus Tuscarora comprises seven of the ten observed species of Tuscarorida, all seven agreeing in the possession of three perradial feet, which alternate originally (in four species), with three interradial teeth surrounding the mouth. The latter is armed in two other species with two teeth, and in one species with four teeth (compare above, p. 1704). The three perradial feet have a similar position as in the tripodal Nassellaria, so that they may be distinguished as an odd caudal foot and two paired lateral feet.

Subgenus 1. Tuscarantha, Haeckel.

Definition.—Shell with three perradial equidistant feet and three interradial equidistant circoral teeth, alternating regularly with the former.

1. Tuscarora bisternaria, John Murray (Pl. 100, figs. 1, 1a).

Shell subspherical, with three lateral perradial feet in the equatorial zone, and three basal interradial teeth around the mouth, alternating regularly with the former. The three lateral feet arise either in the equator itself or a little above it, and are nearly horizontally expanded, descending a little towards the aboral pole. They are straight, cylindrical, twice to four times as long as the shell, geniculate at the inflated base, and covered with small thorns. A circle of six to eight basal pores in the base of each foot. The narrow mouth is triangular, surrounded by the thorny, inflated, subspherical bases of the three long, cylindrical, diverging, thorny teeth, which ascend obliquely and are longer than the shell; each tooth exhibits in the upper part of the inflated base a corona of eight to ten ovate holes.

Dimensions.—Length of the shell 2.0, breadth 1.5.

Habitat.—Central Pacific, Station 264, depth 3000 fathoms.

2. Tuscarora murrayi, n. sp. (Pl. 100, fig. 2). John Murray, 1876, L. N. 27, pl. 24, fig. 4.

Shell pear-shaped, with three circoral perradial feet in the upper third and three basal interradial teeth around the mouth. The three lateral feet are thin, cylindrical, arcuate, very bristly, arise immediately beyond the narrow tubular peristome, and ascend obliquely nearly to the height of the mouth; then they are curved downwards in a large arc, three to four times as long as the shell. The tubular peristome is about half as long as the shell, bottle-shaped, nearly three-sided prismatic, and bears three very long spinulate teeth, which in the lower half are parallel, in the upper slightly curved and diverging, at the base pear-shaped. Three ovate basal pores in the inflated base of each foot and each tooth.

Dimensions.—Length of the shell 2.5, breadth 1.5.

Habitat.—South Pacific, Station 295, depth 1500 fathoms.

3. Tuscarora wyvillei, n. sp. (Pl. 100, figs. 3, 3a-3c).

Shell subspherical, pellucid, thinner and more fragile than in the other species of the genus, with three aboral perradial feet in the lower third, and three interradial teeth around the wide mouth. The three feet are straight, conical, widely divergent, shorter than the shell, and arise from its lower third; on the inflated base of each four small ovate pores. The three teeth, alternating with them, are straight, cylindrical, arise from the margin of the mouth and diverge obliquely upwards. On the base of each foot four opposite cordate pores of very unequal size.

Dimensions.—Length of the shell 1.5, breadth 1.4.

Habitat.—South Pacific, Station 291, depth 2250 fathoms.

4. Tuscarora tetrahedra, John Murray (Pl. 100, figs. 4, 4a).

Shell tetrahedral or three-sided pyramidal, with three perradial basal feet, and three alternate, interradial, circoral teeth. The three rounded edges of the pyramid are prolonged directly over the aboral base into the three short, divergent, conical, basal feet, which are smooth and scarcely one-fourth as long as the shell. The base of each foot is pierced by four small crossed pedal pores. The narrow mouth, on the apex of the pyramid, is surrounded by three short and broad, triangular, spinulate teeth, each of which bears three slender, triangular, dental pores.

Dimensions.—Length of the shell 2.5, breadth 2.0.

Habitat.—Tropical Atlantic, Station 348, depth 2450 fathoms.

Subgenus 2. Tuscaretta, Haeckel.

Definition.—Shell with three perradial equidistant feet, and with two circoral teeth, which are opposite in the radius of the odd dorsal foot; therefore a dorsal and a ventral tooth.

5. Tuscarora tubulosa, John Murray (Pl. 100, figs. 5, 5a, 5b).

Shell subspherical, with three lateral perradial feet on the upper half of the shell (above the equator), and two parallel vertical teeth on the mouth. The three feet arise between the upper and the middle third of the shell, diverge upwards, and are slightly arcuate, covered with numerous curved spines. Their base is pierced by four pedal pores. The peristome is a narrow sagittal fissure, placed in the radius of the odd or dorsal foot, and bears two opposite teeth on its two corners. The teeth are cylindrical, longer than the shell, covered with curved spines, and ascend in a parallel and vertical manner; each is perforated at the base by three large dental pores.

Dimensions.—Length of the shell 1.4, breadth 1.2.

Habitat.—North Pacific, Stations 244 to 250, depth 2050 to 3050 fathoms.

6. Tuscarora porcellana, John Murray (Pl. 100, figs. 6a, 6b).

Shell pear-shaped, with three lateral perradial feet in the lower half of the shell, and two parallel vertical teeth on the mouth. The three lateral feet arise between the middle and the lower third of the shell, are straight, cylindrical, spinulate, about as long as the shell and diverge downwards; their base is pierced by four ovate pedal pores. The two parallel and vertical teeth are straight, shorter than half the shell, and opposite in the sagittal plane, on the two corners of the narrow mouth, in the radius of the dorsal odd foot. The base of each tooth exhibits four cordate dental pores.

Dimensions.—Length of the shell 1.5, breadth 1.3.

Habitat.—South Atlantic, Station 325, depth 2650 fathoms.

Subgenus 3. Tuscarilla, Haeckel.

Definition.—Shell with three perradial equidistant feet, and with four crossed equidistant teeth around the mouth.

7. Tuscarora belknapii, John Murray.

Shell pear-shaped, with three lateral perradial feet in the upper third, and four crossed teeth around the mouth. The three arcuate feet are thin, cylindrical, covered with small curved thorns, and arise at the base of the peristome, between the upper and middle third of the shell; they ascend diverging to the height of the mouth, and are then curved downwards in a large arc, twice to three times as long as the shell. The base of each foot is dilated and pierced by three pedal pores. The four thin and long teeth of the peristome are similar to the feet, ascend in a slightly diverging manner, and are so placed that two opposite lie in the sagittal plane (or in the radius of the dorsal odd foot), whilst the two others are opposite in the frontal plane (perpendicular to the former). The base of each tooth exhibits two large ovate dental pores.

Dimensions.—Length of the shell 2.5, breadth 1.5.

Habitat.—South Pacific, Station 293, depth 2025 fathoms.

Genus 718. Tuscarusa,^[334] n. gen.

Definition.—Tuscarorida with four radial aboral feet and a variable number of circoral teeth.

The genus Tuscarusa differs from the preceding closely allied Tuscarora in the possession of four radial feet instead of three. The mouth of the single observed species is a narrow sagittal fissure, and armed with two opposite teeth (a dorsal and a ventral, as in the subgenus Tuscaretta). The four lateral feet form a cross, and lie opposite in pairs, in two diagonals of the square, which is bisected by the sagittal mouth.

1. Tuscarusa medusa, n. sp. (Pl. 100, figs. 7, 7a).

Shell ovate, with four crossed lateral feet in the upper third, and with two opposite teeth around the mouth. The four feet are opposite in pairs in two diameters of the shell, perpendicular one to another, and arise between the upper and middle third of the shell; they are thin, cylindrical, spinulate, arcuate, and ascend to the height of the mouth diverging upwards; then they are curved downwards in a large arc. They lie in the diagonals of the square, which is halved by the narrow and long fissure of the mouth. This lies in the original sagittal plane, and from its two corners arise the two opposite teeth (a dorsal and a ventral), diverging upwards, cylindrical and slightly curved. The base of each foot is pierced by four pedal pores, of each tooth by two dental pores.

Dimensions.—Length of the shell 1.2, breadth 1.0.

Habitat.—North Pacific, Station 253, depth 3125 fathoms.

Genus 719. Tuscaridium,^[335] n. gen.

Definition.—Tuscarorida without radial aboral feet, but with a terminal axial caudal foot, and a variable number of circoral teeth.

The genus Tuscaridium, comprising two closely allied species, differs from the two preceding genera of Tuscarorida in the absence of lateral radial feet, which are represented by a single large caudal spine placed in the main axis of the shell, at its aboral pole. The shell is therefore spindle-shaped, and not ovate or subspherical, as in the two other genera. It reaches in the two observed species a length of more than 3 mm.

1. Tuscaridium cygneum, Haeckel.

Shell spindle-shaped, twice as long as broad (in the transverse section circular), equally tapering towards both poles of the main axis. The aboral pole bears a thin, cylindrical, straight, caudal spine, placed in the prolongation of the main axis, and about half as long as the shell. Its base is pierced by two large opposite pedal pores. The anterior or oral pole bears a cylindrical peristome, similar to a bird's head, and curved towards the ventral face; on both sides of its neck (at right and left) a series of three or four irregular, ovate, buccal holes. The neck bears four cylindrical, spinulate, radial tubes (two on each side), crossed nearly horizontally, and placed in two diagonal planes perpendicular one to another; these planes correspond to those in which the four feet of Tuscarusa medusa lie. The base of each tube is pierced by four dental pores.

Dimensions.—Length of the shell 3.2, breadth 1.6.

Habitat.—North Pacific, Station 250, depth 3050 fathoms.

2. Tuscaridium lithornithium, n. sp. (Pl. 100, figs. 8, 8a, 8b).

Shell spindle-shaped, twice as long as broad, very similar to the preceding closely allied species. It differs from the latter in the following characters:—The curved proboscis of the peristome is broader and more spiny. The four radial tubes of the mouth and the terminal caudal spine are very spiny (in the preceding species nearly smooth). The number of buccal holes (six to eight on each side of the mouth) is twice as great as in the former. Each circoral tube is pierced at the base by six or eight (in the former by four pores), and the base of the caudal spine exhibits a cross of four pores (in Tuscaridium cygneum only two pores).

Dimensions.—Length of the shell 3.6, breadth 1.8.

Habitat.—North Pacific, Station 264, depth 3000 fathoms.

Order IV. PHÆOCONCHIA, Haeckel, 1879.

Definition.—Phæodaria with a bivalved lattice-shell, composed of two free opposite valves (a dorsal and a ventral), between which the central capsule is enclosed.

Family LXXXIII. Concharida, Haeckel, 1879 (Pls. 123-125).

Definition.—Phæodaria with a bivalved lattice-shell, which is spherical or lenticular, and composed of two equal or unequal boat-shaped valves, a dorsal and a ventral. The valves bear neither an apical latticed cupola or galea, nor hollow radial tubes. The central capsule is placed in the aboral half of the shell-cavity, and so enclosed between both valves, that its three openings lie in the open frontal fissure between them (the astropyle on the oral pole of the main axis, the two parapylæ on both sides of its aboral pole, at right and left).

The family Concharida and the two following closely allied families, the Cœlodendrida and Cœlographida, compose together the most remarkable and interesting suborder of Phæoconchia (or "Phæodaria bivalva"), differing from all the other Radiolaria in the possession of a bivalved lattice-shell, composed of two separate valves, like the shell of a Brachiopod. The central capsule is so enclosed between the two fenestrated valves that its three openings lie in the horizontal open (frontal) fissure between them, the astropyle or main-opening on the oral pole of the main axis; the two secondary openings or parapylæ on the two sides of its aboral pole, at right and left. The plane in which the three openings lie is therefore the frontal plane, dividing the entire body into a dorsal and a ventral half. The two valves, accordingly, must be considered as dorsal and ventral valves (as in the Brachiopoda), and the symmetrical halves of each valve as right and left. These halves may be always easily distinguished, since the oral pole of each valve is constantly different from the aboral pole. The voluminous phæodium always lies in the oral half, and the central capsule in the aboral half of the shell-cavity, whilst the calymma encloses the whole shell.

The Concharida differ from the other two families of bivalved Phæodaria in the absence of the apical galeas, and the branched hollow tubes arising from them. Each of these two cupolas, which are at the opposite poles of the sagittal axis (one cupola on the apex of each valve), is in the Cœlographida connected by a simple or double frenulum with a peculiar rhinocanna, or an open nasal tube directed towards the mouth; whilst the cupolas of the Cœlodendrida possess neither a rhinocanna nor a frenulum. The three families of Phæoconchia may therefore represent a phylogenetical series, the common root of which are the Concharida. From these are developed the Cœlodendrida by development of an apical cupola or galea on each valve, and of hollow radial tubes arising from it; whilst the Cœlographida are developed from the latter by production of a rhinocanna on the base of each cupola, and of one or two frenula connecting the former with the latter.

All the Concharida described in the following pages (seven genera and thirty species), are perfectly new to science, and not a single form of this interesting family was known before the explorations of the Challenger. Some species (mainly of the genera Conchidium and Conchopsis) are by no means rare, and are found in great numbers at some stations of the tropical seas (in the Pacific as well as in the Atlantic). All described species are closely allied, agree in the majority of characters, and are easy to distinguish from all the other Radiolaria. Some few forms of Concharida, however, form a direct passage to the Cœlodendrida.

Regarding the probable origin of the Concharida (and therefore also of all other Phæoconchia derived from the latter), two different hypotheses are possible. They have either been derived directly from the skeletonless Phæodina, by development of a bivalved lattice-shell; or they may be derived from Phæodaria with a simple spherical lattice-shell (Castanellida), by the halving of this latter, or its splitting into two hemispherical valves; the former hypothesis is more probable than the latter.

The two valves of the lattice-shell (Pls. 123-126) must in the Concharida (as in all other Phæoconchia) be distinguished as dorsal and ventral, and may therefore be compared with the two valves of the Brachiopoda, not with those of the Lamellibranchia. This important morphological distinction is expressed by the constant position of the central capsule within the shell-cavity. The capsule always exhibits the character of the "Tripylea" and has three tubular openings, placed in the frontal or lateral plane of the unicellular body. In the same plane lies the open frontal fissure between the two valves, and the three openings are so disposed in it that the large anterior main-opening (or the astropyle) is placed on the oral pole of the main axis, whilst the two accessory small lateral openings or parapylæ are placed on both sides of the aboral pole, at the right and left. Therefore in a dorsal or ventral view all three openings are visible (Pl. 123, figs. 1, 8a); in the usual lateral view, however, from the right or left side, only two openings are visible, the astropyle on the anterior, and one parapyle (right or left) near the posterior pole of the main axis (Pl. 123, figs. 8, 9; Pl. 124, figs. 6, 10). The posterior view (from the aboral pole) shows the two parapylæ, at right and left; in the anterior view (from the oral pole) the astropyle may be visible, but usually it is completely hidden in the dark voluminous phæodium. This latter envelops sometimes nearly the whole capsule as an opaque conglomeration of green or brown phæodella (Pl. 123, figs. 8, 9); but usually the phæodium fills up the anterior (oral) half of the shell-cavity, whilst the capsule occupies the posterior (aboral) half (Pl. 124, figs. 6, 10).

The dorsal shell-valve is in almost all Phæodaria smaller or somewhat different in shape from the ventral valve, and this difference is often very striking (Pl. 124, figs. 3-16); but in a few species both valves are so similar, that I could not discover any certain difference. This equality of the two valves occurs mainly in those Concharida which pass over into the Cœlodendrida; in these latter as well as in the Cœlographida, both valves are usually equal in size and form. Whilst the main axis (or the longitudinal axis of the body) in the two latter families of Phæoconchia seems to be normally vertical (in the living and freely floating body), in the living Concharida it is probably horizontal, so that the larger and heavier ventral valve lies below the smaller and lighter dorsal valve.

The geometrical fundamental form of the body is therefore in the Concharida dipleural or bilaterally symmetrical, and we distinguish in it the same three dimensive axes, as in all other dipleural forms. On the anterior or oral pole of the main axis (or longitudinal axis) lies the mouth of the shell, and behind it the phæodium; on the opposite posterior or aboral pole lies the hinge of the shell (comparable to the shell-hinge of the Brachiopoda) and in front of it the central capsule. The sagittal (or dorso-ventral) axis, determining the height of the shell, has on its dorsal (or upper) pole the apex or highest point of the dorsal valve, on its ventral (or lower) pole the apex or lowest point of the ventral valve. The two poles of the frontal (lateral or transverse) axis are equal and are determined by the two parapylæ of the capsule, and the corresponding points of the shell-fissure between both valves. Usually the main-axis is the longest, the frontal axis the shortest, and between both the sagittal axis.

In regard to the three dimensive planes which are determined by these three axes, perpendicular to one another, they are rarely of nearly equal size (as in some subspherical species), usually the sagittal plane (separating the right and left halves of the body) is the largest; the cinctural or equatorial plane (separating oral and aboral halves) is the smallest, and the frontal or lateral plane (separating dorsal and ventral halves) is intermediate in size. The relation of the three perimeters of these three planes corresponds to that proportion; the sagittal perimeter (in which the keel of the compressed valves lies) is the largest; the cinctural or equatorial perimeter (separating the anterior phæodium and the posterior central capsule) is the smallest, and the frontal or lateral perimeter (in which the fissure between the valves lies) is intermediate in size.

The general form of the single valves is very varied in the different species, in the majority boat-shaped or hat-shaped, more or less laterally compressed, in a few forms hemispherical. In Conchopsis (Pl. 125) and Conchoceras (Pl. 124, figs. 15, 16) the lateral parts of the valves (right and left) are vaulted, whilst their median parts are so strongly compressed that they form a sharp sagittal keel, and then the shell in the dorsal or ventral view appears spindle-shaped (Pl. 123, fig. 8a; Pl. 125, fig. 8). Often the frontal margins of the valves are somewhat constricted (Pl. 124, fig. 7).

The junction between the two valves of the shell is always loose, but not so loose as in the two following families. In the Cœlodendrida and Cœlographida the two valves are either perfectly free and separated by a frontal zone of jelly, or in very loose contact on the frontal margins. In the Concharida, however, the margins of both valves seem to be usually in contact, and their connection is effected in a double way. In the subfamily Conchasmida (comprising the genera Concharium and Conchasma, Pl. 123, figs. 1-6) the lateral margins of both valves are smooth, not dentated, and fit one into another like the two parts of a box, or like the two valves of a Diatom (Navicula). In the second subfamily, however, Conchopsida (comprising the five other genera, Pls. 124, 125), the lateral margins of the valves are dentate, usually provided with a series of numerous strong conical teeth, and the teeth of both valves so catch into one another, that their union is rather firm (like the margin of the shells of Tridacna, Pecten, and other Lamellibranchiata). Besides, a more solid junction is often effected on the posterior or aboral part of the margins, which we shall call the hinge. Here often peculiar strong teeth catch one into another, and in the majority of species two aboral spines are developed, the caudal horns (a dorsal and a ventral); these are very large in Conchoceras (Pl. 124, figs. 15, 16). But a peculiar and most interesting kind of junction is effected in some Concharida by a true ligament between the valves (Pl. 123, figs. 8, 9; Pl. 125, fig. 2). This ligament is always placed on the aboral hinge, is of dark brown colour, and is not dissolved by mineral acids unless long applied. It may preserve the connection of the posterior parts of both valves, when their anterior parts are removed one from another, just as in the Brachiopoda. I observed this interesting ligament mainly in the genus Conchopsis, but not in all species, and it is not yet certain whether it is a constant organ in these and some other Concharida.

In the majority of Concharida the lateral margins of the two valves project slightly inwards into the cavity, and in some species of Conchopsis these inner borders are so broadened that they form a broad, horizontal, fenestrated inner shelf, comparable to the deck of a boat or to the velum of the Hydromedusæ or Craspedotæ (Pl. 125, fig. 9). In this case the velum surrounds the ovate aperture through which the two lobes of the central capsule (dorsal and ventral) enter into the cavity of both valves.

The mouth of the shell lies on the oral pole of the main axis, and is therefore opposed to the aboral hinge. The two valves are here usually more or less emarginate, so as to form a transverse mouth with an upper and a lower lip (Pl. 124, figs. 6, 7, 11). The form of these two lips is often very different and characteristic of particular species (Pl. 124, figs. 3, 15, 16). The mouth remains in many species constantly open, even when the frontal fissure is closed (figs. 7, 16). Since the centre of the shell mouth lies in the prolongation of the proboscis arising from the operculum of the central capsule, probably the main stream of sarcode, issuing from the latter, becomes protruded by the former.

Apophyses of the shell (besides the teeth of the margins) are completely wanting in three genera, Concharium, Conchellium, and Conchopsis (Pl. 123, figs. 1-4, 7; Pl. 125). The four other genera possess free apophyses or spines, which we call horns. They are probably important as the beginnings of those large hollow tubes which are characteristic of the two following families, Cœlodendrida and Cœlographida. We distinguish two different forms of horns, apical horns on the poles of the sagittal axis, and caudal horns on the aboral pole of the main axis; the former probably correspond to the sagittal tubes and the latter to the caudal tubes of the two following families. Apical horns are found in a single genus only, Conchonia (Pl. 124, figs. 10-14). Here either on one pole or on poles of the sagittal axis a horn is developed, usually curved backwards. Sometimes the base of this conical horn is inflated and fenestrated, and may represent the beginning of the formation of the galea or apical cupola of the Cœlodendrida.

The two caudal horns are opposite on the aboral hinge of the shell, one arising from the posterior end of each valve. Usually they are short and thick, pyramidal, the ventral horn larger than the dorsal (Pl. 124, figs. 3, 6). Rarely the two caudal horns are fenestrated at the base and reach a considerable size, as in Conchoceras (Pl. 124, figs. 15, 16).

The walls of the bivalved shell usually exhibit in the Concharida a rather solid shape and regular structure, with an elegant network of regularly arranged pores. But in some species the walls of the shell become very thin and fragile, and assume the same shape (with very irregular network), as in the Cœlodendrida and Cœlographida. The pores are usually small and numerous, circular, often hexagonally framed (Pl. 125, figs. 4-6). They pierce the thick shell-wall either in a radial or in an oblique direction. Sometimes each pore is armed with six radial teeth (Pl. 123, fig. 7a). At other times each pore represents an oblique ampullaceous canal, dilated in its middle part, with two narrow openings (Pl. 125, figs. 5a, b, c, 6). The pores are so arranged in the majority of species that they form regular curved series, which are separated by prominent crests, and converge towards the poles of the main axis. Usually the marginal pores (along the frontal margin of the valves) are much smaller (compare Pls. 123-125).

The central capsule of the Concharida, very well preserved in numerous specimens of the Challenger collection, constantly possesses the same situation and structure. It is always enclosed in the aboral or posterior half of the shell-cavity, whilst the oral or anterior half is filled up by the phæodium. The free spaces between both and between the inner surface of the shell are completely filled up by the jelly of the calymma, which also covers the whole shell as a thin outer jelly-envelope. The form of the central capsule is sometimes nearly spherical, usually somewhat compressed in the direction of the main axis, and sometimes also in the direction of the frontal axis (Pl. 123, figs. 1-9). In some species it becomes bilobed, with an upper dorsal and a lower ventral lobe, and in some others it becomes triangular (Pl. 125, fig. 7). Its two membranes (inner and outer) are often separated by a broad colourless interval, containing a clear fluid or jelly (Pl. 123, figs. 8, 9). The nucleus is usually about half as large as the central capsule and ellipsoidal, its longer axis lying in the sagittal diameter of the body. Several specimens (of different genera) contained two separate nuclei, one placed in the dorsal, the other in the ventral half of the capsule (Pl. 124, fig. 6). This duplication of the nucleus is probably the preparation for the division of the capsule. The division will be probably effected in the frontal plane, so that each half of the bisected capsule gets one nucleus and one valve, and the other valve becomes newly formed (in a way similar to that in the bivalved Diatomaceæ). The astropyle, or the main-opening of the capsule, is closed by a radiate operculum, from which arises a tubular proboscis; this lies in the main axis of the body, is directed towards the anterior mouth of the shell, and surrounded by the phæodium. The two shorter tubes of the paired parapylæ, or the accessory lateral openings, lie on the posterior or caudal side of the capsule, at right and left, and are directed half backwards, half outwards (towards the frontal fissure between the valves, Pl. 123, figs. 1, 8a).

The phæodium exhibits in all Concharida the same characteristic shape, and represents a dark conglomeration of phæodellæ, filling up the anterior or oral half of the shell-cavity. Usually it is bilobed, divided into a dorsal and a ventral lobe or wing, which fills up the corresponding valve of the shell (Pl. 123, figs. 8, 9). The phæodium is commonly more voluminous than the capsule, and surrounds its anterior half, more rarely it encloses nearly the entire capsule (Pl. 124, figs. 6, 10). Its colour is usually olive, sometimes more greenish, at other times more brownish, in some species nearly black. The phæodellæ, or the roundish granules which compose the phæodium, exhibit the same shape as in all other Phæodaria (compare above, p. 1535). Sometimes peculiar rather oblong nucleated cells are scattered in great numbers between the phæodellæ, probably parasites or symbiontes (Pl. 123, figs. 7-9, 9a).

Synopsis of the Genera of Concharida.

Subfamily 1. Conchasmida, Haeckel.

Definition.—Concharida with the lateral margins of the two valves smooth, without interlocking teeth.

Genus 720. Concharium,^[336] Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 6.

Definition.—Concharida with the lateral margins of the valves smooth, without sagittal keel and without horns on the hinge.