14. Gazelletta dendronema, n. sp. (Pl. 120, fig. 16).

Shell hemispherical, thorny, with a broad, alveolate velum which bears irregular hollow thorns on the inside and on the free margin (fig. 16). Feet divergent, irregularly curved, with scattered arborescent lateral spines, which are irregularly branched, and bear at the distal end of each branch a small spathilla with four to six teeth. The distal ends of the feet are dichotomously branched, with stouter simple fork-branches.

Dimensions.—Length of the shell 0.17, breadth 0.36; length of the feet 0.5 to 0.7.

Habitat.—North Pacific, Station 252, surface.

15. Gazelletta melusina, n. sp. (Pl. 118, fig. 1).

Shell campanulate, spiny. Feet divergent, strongly curved, with scattered arborescent lateral spines, which are richly and dichotomously branched, with thin, simple, terminal branches. The distal ends of the feet bear three or four much larger and stouter branches, which are again dichotomously branched.

Dimensions.—Length of the shell 0.2, breadth 0.15; length of the feet 0.5 to 0.8.

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

Genus 703. Gorgonetta,^[320] n. gen.

Definition.—Medusettida with twelve articulate feet on the peristome, six ascending and six alternate descending.

The genus Gorgonetta is the most highly developed of all hitherto observed Medusettida, and belongs to the most remarkable forms of Radiolaria. Its general shape is very similar to that of a larva of a Geryonia or Carmarina, in which six interradial larval tentacles are directed upwards, six alternating perradial permanent tentacles downwards. The six ascending feet are in all the four species observed smaller, more or less branched, and armed with spathillæ. The six descending feet are much larger and covered with very elegant pencils, the single threads of which bear a double spathilla. The distal ends of the feet are forked or branched.

1. Gorgonetta mirabilis, n. sp. (Pl. 119, figs. 1-4).

Shell cap-shaped, flatly vaulted, or nearly hemispherical, about twice as broad as long, with smooth surface. Six ascending feet widely divergent, about twice as long as the breadth of the shell, nearly straight, arborescent, with numerous curved branches, each of which bears at the distal end a spathilla with four to six short recurved teeth (fig. 2). Six descending feet about twice as long as the six alternate ascending, nearly straight, covered with numerous elegant pencils. Each pencil is richly branched, with fifty to one hundred or more thread-like ramules, and each terminal ramule has two cruciate spathillæ, a larger proximal and a smaller distal (figs. 3, 4); the four recurved anchor-teeth of the proximal spathilla are twice as large as those of the distal. The distal end of each descending foot bears three or four very stout terminal branches, each of which is about as long as the shell and again trifurcate at the distal end.

Dimensions.—Length of the shell 0.2 to 0.3, breadth 0.4 to 0.5.

Habitat.—Tropical Atlantic, Stations 346 to 348, surface.

2. Gorgonetta geryonia, n. sp.

Shell hemispherical, twice as broad as long, with short scattered thorns on the surface. Twelve feet of similar shape to those in the preceding species, but differing in the following characters:—the six ascending feet are much smaller, about as long as the breadth of the shell, and each bears only six to twelve short branches; the six descending feet are about three times as long as the shell, more or less curved; their pencils much smaller, and the two spathillæ of each pencil-thread bear five anchor-teeth. The distal ends are more richly and irregularly branched.

Dimensions.—Length of the shell 0.4, breadth 0.7.

Habitat.—Indian Ocean (Cocos Islands), Rabbe, surface.

3. Gorgonetta carmarina, n. sp.

Shell flat, cap-shaped, three times as broad as long. Twelve feet similar in shape to those of the two preceding species, but more irregular in form and arrangement, and differing in the following characters:—the six ascending feet are nearly horizontally expanded, one and a half times as long as the breadth of the shell, with few short branches, each of which bears a spathilla with six recurved anchor-teeth. The six descending feet are about five times as long as the shell, irregularly curved, studded with numerous small pencils, each thread of which bears a double spathilla with six teeth. The distal ends are irregularly branched.

Dimensions.—Length of the shell 0.2, breadth 0.7.

Habitat.—South Pacific, Station 318, depth 2040 fathoms.

4. Gorgonetta bisenaria, n. sp.

Shell campanulate, similar to that of Gazelletta melusina (Pl. 118, fig. 1), with smooth surface. Six ascending feet about as long as the shell, nearly straight, similar to those of Gorgonetta mirabilis (Pl. 119, fig. 1). Six descending feet also similar to those of the latter, but shorter, about twice as long as the shell, strongly curved, studded with numerous small pencils, each thread of which has a double spathilla with three teeth. The distal end of each foot bears a whorl of six to eight irregular forked branches.

Dimensions.—Length of the shell 0.5, breadth 0.4.

Habitat.—Central Pacific, Station 263, surface.

Genus 704. Polypetta,^[321] n. gen.

Definition.—Medusettida with numerous (ten to twenty or more) articulate feet.

The genus Polypetta comprises those Medusettida in which the number of feet is very large and not limited, usually twenty to thirty or more. The few specimens of this genus that have been observed are rather different; and it may be that only the two first species described in the following lines are true Medusettida; they possess the usual distinctly alveolate feet, and are derived from the similar Medusetta or Gazelletta simply by multiplication of the feet. The two other species, however (figured in Pl. 116, figs. 1, 2, as Porospathis), belong perhaps to another family of Phæodaria (Castanellida?); their shell-structure is peculiar and their feet not distinctly alveolate; they may therefore represent a peculiar genus Porospathis (Haeckel, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, 1879, p. 5).

1. Polypetta polynema, n. sp.

Shell campanulate, thorny, about as long as broad, with slightly constricted mouth, similar to that of Gazelletta orthonema (Pl. 120, fig. 10). Shell-wall hollow, with irregular polygonal alveoles. Peristome with a corona of eighteen divergent, curved, cylindrical feet of unequal size; six larger primary on the margin of the shell, the other twelve secondary, between the former, somewhat above the margins at different heights. The feet are two to three times as long as the shell, irregularly curved and distinctly alveolate, without appendages.

Dimensions.—Length of the shell 0.12, breadth 0.11.

Habitat.—Central Pacific, Station 266, surface.

2. Polypetta alveolata, n. sp.

Shell campanulate, thorny, about as long as broad, very similar to that of Medusetta craspedota (Pl. 120, fig. 4). Shell-wall hollow, with subregular hexagonal alveoles. Peristome prolonged into a short funnel-shaped proboscis, twice as long as the similar velum of the latter. The velum is surrounded by a corona of eight larger and eight to twelve smaller feet; the larger are about as long as the shell, divergent, irregularly curved, thorny, and distinctly alveolate; the smaller feet are scattered above the latter and form an immediate transition to the small spines of the shell-surface.

Dimensions.—Length of the shell 0.08, breadth 0.09.

Habitat.—South Pacific, Station 284, surface.

3. Polypetta tabulata, n. sp. (Pl. 116, figs. 2, 2a, 2b).

Shell subspherical, with elegantly panelled or tabulate surface, composed of small triangular plates, which are separated by a network of prominent crests; at each nodal point of the network a small conical thorn arises (figs. 2a, 2b). Each triangular plate seems to contain a hollow alveole, which opens into the shell-cavity (?). On the surface of the shell are scattered numerous (thirty to forty or more), cylindrical, hollow, radial spines, which are straight or slightly curved, not distinctly alveolate, and increase in size towards the mouth. The aboral spines are scarcely one-third as long as the radius of the shell, whilst the oral spines are three times as long as its diameter. The proboscis of the constricted mouth is a hollow cylinder, longer than the shell-radius, and armed with a corona of fifteen to twenty slender bristle-shaped teeth. The position of this singular species in this family is doubtful.

Dimensions.—Diameter of the shell 0.1 to 0.11, length of the peristome 0.07, breadth 0.02.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

4. Polypetta mammillata, n. sp. (Pl. 116, figs. 1, 1a).

Shell subspherical, densely covered with numerous mammiliform hollow papillæ, between which are scattered single longer, hollow, radial spines; these are irregularly curved, cylindrical, without distinct alveoles; the twelve longest are two to three times as long as the shell, divergent in the oral direction, and surround the base of the peristome in two irregular alternate circles, each with six spines. The hollow papillæ of the surface, between which are placed numerous circular pores (or dimples?), open into the shell-cavity by a small pore (fig. 1a); they are perhaps reduced radial spines. The constricted peristome is conical and prolonged into an inversely conical proboscis, which is about as long as the radius of the shell; its dilated mouth is surrounded by a corona of slender, divergent, bristle-shaped teeth. The position of this species in the family Medusettida is doubtful; perhaps it is more closely allied to the Castanellida.

Dimensions.—Diameter of the shell 0.12; length of the proboscis 0.08, breadth 0.03; length of the shorter spines 0.1, of the longest spines 0.3.

Habitat.—North Pacific, Station 252, surface.

Family LXXX. Castanellida, Haeckel, 1879 (Pl. 113).

Definition.—Phæodaria with a spherical or subspherical shell, exhibiting ordinary lattice-work, with circular or roundish pores. Radial spines without circles of basal pores. Mouth of the shell large, usually circular and armed with teeth. Central capsule excentric, placed in the aboral half of the shell-cavity.

The family Castanellida represents a common and widely distributed group of Phæodaria, which posses a very simple and uniform shell, viz., a simple lattice-sphere with radial spines and one simple mouth. It may therefore be easily confounded with the Coscinommida, or those Sphæroidea in which the shell is also a simple lattice-sphere armed with radial spines (Astrosphærida simplicia, p. 209). Indeed the shell of both groups is very similar, and differs in one important point only; the Castanellida constantly possess one larger opening in the shell-wall, the shell-mouth, which is either smooth or armed with a corona of teeth; in the Coscinommida, however, such a mouth is never present. The living specimens of both groups, and those shells in which the soft body is preserved, are very easily distinguished, since the shell encloses in the Coscinommida the central capsule and the transparent calymma only, whilst the latter, besides, in the Castanellida contains a voluminous dark brown or green mass of phæodella, the characteristic phæodium. A closer examination of the central capsule reveals in all Castanellida the typical operculum, the astropyle, with the proboscis of the Phæodaria, which is never present in any Sphæroidea.

The Castanellida are easily distinguished also from those similar Phæodaria in which the shell is also a lattice-sphere; the lattice-work is constantly quite simple, as in the similar Coscinommida, never composed of separated tangential pieces (as in the Aulosphærida), or of porcellanous structure, with basal circles of pores (as in the Circoporida), or of diatomaceous structure (as in the Challengerida). The gigantic Orosphærida, which also in part posses a simple lattice-sphere, differ from the Castanellida in the absence of the peculiar shell-mouth.

Though the Castanellida belong to the most common Phæodaria, and though the number of individuals, floating on the surface of the tropical seas, is extraordinarily great, their variety of forms is very small; the six genera distinguished in the following system differ only in very slight characters, and the majority of the species are very similar, and often hardly distinguishable. The seven species figured in Pl. 113 exhibit the most striking differences which I could distinguish among all the species observed. The shell usually has the characteristic appearance of a chestnut, a sphere covered with very numerous short radial spines or bristles. In the majority of species a certain number of longer thin radial spines is scattered over the surface; these are usually simple, rarely branched. The mouth of the shell, corresponding to the proboscis of the central capsule, and placed in the same radius, is either a quite simple larger opening with a smooth margin (figs. 3, 5, 7) or is armed with a corona of teeth (figs. 1, 6).

The size of the shell varies between 0.2 and 0.8 mm., and is usually between 0.3 and 0.5 mm. Its form is in the majority of species a geometrical sphere; rarely it is somewhat irregular, slightly ellipsoidal (prolonged in the axis of the mouth and proboscis), or polyhedral (by conical protuberances from the bases of the radial spines). The ideal fundamental form of the shell, however, is constantly monaxonian, since the place of the shell-mouth and of the proboscis of the capsule (both lying in one axis of the sphere), causes a principal axis to be different from all others. The longer radial spines, quite variable in number and disposition, are never arranged regularly or symmetrically, and therefore determine no constant axes.

The lattice-work of the spherical shell offers also but slight differences. It is usually more or less irregular, with circular or subcircular pores of unequal sizes. More rarely the network is perfectly regular, with equidistant circular pores of equal size, and sometimes these are surrounded by hexagonal frames (fig. 6), as in many Sphæroidea. More rarely the pores are perfectly irregular, roundish or sometimes polygonal, of unequal sizes and dissimilar forms (fig. 2). The size of the pores is very variable between 0.01 and 0.05, usually between 0.015 and 0.025. They are commonly somewhat broader than the bars between them, more rarely smaller. The substance of the shell-wall is in the the majority of Castanellida hyaline, transparent (as in the similar Sphæroidea); in some larger forms, however, a network of fine axial filaments is visible in the lattice (fig. 2), and sometimes this seems to be hollow, with an axial canal (as in the large Orosphærida). Such an axial filament or fine axial canal is usually visible in the larger radial spines. The shell-wall of the Castanellida, however, never exhibits that characteristic structure (with tangential needles in a cement-like fundamental substance), which we find in all Circoporida. The latter differ also in the constant presence of circles of large pores around the bases of the radial spines, which are never found in the Castanellida. The shell becomes usually stained more or less purple by carmine, and when burned by fire, becomes of a brown colour.

The inner surface of the shell is always quite smooth, the outer surface armed with numerous short and thin radial bristles. Sometimes these bristles or "by-spines" are very short, but never perfectly wanting. Usually their length is about one-third or one-fourth of the radius of the shell, often less, rarely more. They arise from the nodal points between every three or four neighbouring spines, and are commonly very thin and straight, pointed, with slightly thickened conical basis. Rarely they are directed not quite radially, but more or less obliquely.

The larger radial spines, which arise between the thin bristles or "by-spines" and may be opposed to the latter as "main-spines," are wanting in two genera only, in Castanarium and Castanella (Pl. 113, fig. 6). They are simple in Castanidium (figs. 2, 5, 7) and Castanissa (fig. 1), irregularly branched in Castanopsis and Castanura (figs. 3, 4). Their number and disposition is never regular nor symmetrical (as in the majority of Sphæroidea) and varies even in each single species. In general the number of main-spines varies between ten and forty (rarely less or more) usually between twenty and thirty. Their length is commonly about equal to the diameter of the shell, often somewhat shorter, rarely considerably longer. Their thickness is in the majority of species about equal to the diameter of one or two pores of the lattice. Sometimes they are much stronger, rarely thinner.

The form of the radial main-spines is not very variable, usually it is cylindrical or cylindro-conical, rarely angular, prismatic or pyramidal. Sometimes they are straight (perfectly radial), at other times more or less irregularly curved. Usually they are simple, rarely branched; the branches are always very irregular and exhibit a remarkable tendency to unite by concrescence (figs. 3, 4). Some thicker forms of spines exhibit a remarkable structure, the surface being covered with small dimples and spinules between them (fig. 1); sometimes the dimples are hexagonal (fig. 5a). In the axis of the thicker spines there is often visible the same axial filament or funicle which we find in many other Phæodaria, more rarely a hollow axial canal.

The mouth of the shell is usually circular, more rarely polygonal or irregularly roundish (fig. 2). It is either quite smooth (fig. 3, 5, 7) or armed with a corona of strong teeth (figs. 1, 4, 6). These teeth are different from the other spines of the shell; they are much thicker than the radial bristles, and shorter than the main-spines. Their number varies between three and twenty, usually between five and seven. They are usually parallel to the main axis, which is determined by the excentric position of the mouth and the centre of the sphere (figs. 1, 6). The teeth are usually conical, more or less irregular in size and form, more rarely of equal size. The corona of teeth is usually sharply separated from the surrounding lattice-work of the shell, but has no influence on its regular spherical form.

The central capsule of the Castanellida immediately determines beyond doubt their true Phæodarian nature; it lies excentrically in the cavity of the enclosing shell, and is surrounded at the oral pole by the large and dark phæodium. The latter covers the radiate operculum of the capsule membrane and the tubular proboscis, which arises from it and is directed towards the shell mouth. Usually the diameter of the spherical central capsule is about one-third of the shell diameter, rarely one-quarter only, and in a few cases it attains nearly its half. The calymma, therefore, is larger than the capsule, and fills up the whole cavity of the shell which is not occupied by the latter. The greater part of the calymma again is filled up by the dark green or brown, sometimes black phæodella, the roundish granules which compose the voluminous non-transparent phæodium. Sometimes the latter proceeds through the mouth and is partially placed outside the shell (fig. 5).

The astropyle, or the main-opening of the central capsule, is placed on the oral pole of its main axis, while its radiate operculum and the tubular proboscis arising from it possess the same structure as in the other Phæodaria. But the two lateral parapylæ or accessory openings which are present in the majority of the latter seem to be absent in the Castanellida as well as in the Medusettida and the Challengerida. I could never observe a trace of them. The proboscis is a small cylindrical tube and is directed towards the mouth of the shell, therefore placed in its main axis; it is usually quite hidden in the dark phæodium, which occupies the oral half of the shell-cavity, whilst the capsule lies in the aboral half. The large nucleus of the central capsule and its double membrane present the same characters as in the other Phæodaria.

Synopsis of the Genera of Castanellida.

Genus 705. Castanarium,^[322] Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 5.

Definition.—Castanellida without radial main-spines, with a smooth mouth.

The genus Castanarium is the simplest form of all the Castanellida, and may be regarded as the common ancestral form of this family. The simple spherical shell has a smooth, toothless mouth and no larger radial spines; it is densely studded with the simple, radial bristles, which are common to all Castanellida. The shell therefore is very similar to those species of the Astrosphæride Acanthosphæra, which represent the subgenus Rhapidococcus (compare above, p. 210, Pl. 26, fig. 3); it differs from the latter in the possession of the shell-mouth, which is absent in all Sphæroidea.

1. Castanarium darwini, n. sp.

Pores regular, circular, hexagonally framed, three times as broad as the bars. Radial bristles half as long as the radius.

Dimensions.—Diameter of the shell 0.3 to 0.4, of the pores 0.03.

Habitat.—South Atlantic (east of Patagonia), Station 318, depth 2040 fathoms.

2. Castanarium hookeri, n. sp.

Pores regular, circular, hexagonally framed, twice as broad as the bars. Radial bristles one-third as long as the radius.

Dimensions.—Diameter of the shell 0.55, of the pores 0.025.

Habitat.—Indian Ocean, Cocos Islands (Rabbe), surface.

3. Castanarium lyelli, n. sp.

Pores regular, circular, without hexagonal frames, of the same breadth as the bars. Radial bristles twice as long as the diameter of one pore.

Dimensions.—Diameter of the shell 0.24, of the pores 0.015.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms.

4. Castanarium lubbocki, n. sp.

Pores irregularly roundish, about of the same breadth as the roundish, non-crested bars. Radial bristles one-third as long as the radius.

Dimensions.—Diameter of the shell 0.36, of the pores 0.01 to 0.02.

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

5. Castanarium huxleyi, n. sp.

Pores irregularly polygonal, two to three times as broad as the bars, separated by prominent polygonal crests. Radial bristles half as long as the radius.

Dimensions.—Diameter of the shell 0.45, of the pores 0.02 to 0.05.

Habitat.—South Pacific (off Australia), Station 165, surface.

Genus 706. Castanella,^[323] Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 5.

Definition.—Castanellida without radial main-spines, with a dentate mouth.

The genus Castanella comprises the most common and most widely distributed species of Castanellida. It agrees in general shape with its ancestral form, the preceding Castanarium, differing from it only in the possession of strong teeth, which form a corona around the mouth.

1. Castanella wyvillei, n. sp. (Pl. 113, fig. 6).

Pores regular, circular, of equal size, hexagonally framed, of the same breadth as the bars. Radial bristles twice as long as the diameter of one pore. Mouth with five to six parallel, conical strong teeth, which are twice as long as a bristle (fig. 6a).

Dimensions.—Diameter of the shell 0.5 to 0.7, of the pores 0.02 to 0.03.

Habitat.—North Pacific, Stations 252 to 256, surface.

2. Castanella thomsoni, n. sp.

Pores regular, circular, of equal size, hexagonally framed, twice as broad as the bars. Radial bristles about as long as the diameter of one pore. Mouth with four strong, conical teeth, forming a regular cross, four times as long as a bristle.

Dimensions.—Diameter of the shell 0.7 to 0.8, of the pores 0.03.

Habitat.—South Pacific, Stations 295 to 298, surface.

3. Castanella campbelli, n. sp.

Pores regular, circular, hexagonally framed, three times as broad as the bars. Radial bristles half as long as the radius of the shell. Mouth with a coronet of eight conical, parallel teeth, of the same length as the bristles, but four to six times as thick.

Dimensions.—Diameter of the shell 0.4 to 0.45, of the pores 0.025.

Habitat.—Central Pacific, Stations 270 to 274, surface.

4. Castanella sloggetti, n. sp.

Pores subregular, circular, without frames, of different sizes, about twice as broad as the bars. Radial bristles three times as long as one pore. Mouth with five or six strong, conical teeth, twice as long as the bristles.

Dimensions.—Diameter of the shell 0.3 to 0.36, of the pores 0.02 to 0.03.

Habitat.—Tropical Atlantic, Stations 347 to 349, surface.

5. Castanella balfouri, n. sp.

Pores irregular, roundish, two to three times as broad as the bars. Bristles about one-fourth as long as the radius. Mouth with four strong conical teeth, forming a cross, somewhat longer and much thicker than the bristles.

Dimensions.—Diameter of the shell 0.22 to 0.28, of the pores 0.01 to 0.02.

Habitat.—North Pacific, Stations 240 to 245, surface.

6. Castanella channeri, n. sp.

Pores irregular, roundish, two to four times as broad as the bars. Bristles nearly half as long as the radius. Mouth with seven to nine short conical teeth, shorter than the bristles, but much thicker.

Dimensions.—Diameter of the shell 0.3 to 0.4, of the pores 0.02 to 0.025.

Habitat.—North Atlantic, Stations 352 to 354, surface.

7. Castanella horstoni, n. sp.

Pores irregular, polygonal, three to four times as broad as the bars. Bristles about as long as the radius. Mouth with six stout pyramidal teeth, which are scarcely one-third as long as the radius.

Dimensions.—Diameter of the shell 0.55, of the pores 0.02 to 0.025.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.

Genus 707. Castanidium,^[324] Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 5.

Definition.—Castanellida, with simple radial main-spines and a simple smooth mouth.

The genus Castanidium agrees with its ancestral form Castanarium in the simple shape of the smooth and toothless mouth, but differs from it in the possession of long radial main-spines, which are scattered between the constant radial bristles or by-spines of the surface. The shell agrees therefore in its general shape with the Astrosphæride Heliosphæra, as defined above (p. 217, Pl. 26, fig. 9), but differs from it in the possession of the shell-mouth wanting in all Sphæroidea.

1. Castanidium willemoesi, n. sp.

Pores regular, circular, hexagonally framed, twice as broad as the bars. Bristles three times as long as the diameter of one pore. Radial main-spines straight, conical, smooth, as long as the radius.

Dimensions.—Diameter of the shell 0.3 to 0.4, of the pores 0.012 to 0.016.

Habitat.—Central Pacific, Station 263 to 274, surface.

2. Castanidium wildi, n. sp.

Pores regular, circular, hexagonally framed, of the same breadth as the bars. Bristles twice as long as one pore. Radial main-spines straight and short, cylindrical, with dimpled surface (as in Pl. 113, fig. 1), as broad as one pore and as long as the diameter of the shell.

Dimensions.—Diameter of the shell 0.66, of the pores 0.045.

Habitat.—South Pacific, Station 297, surface.

3. Castanidium buchanani, n. sp. (Pl. 113, fig. 7).

Pores regular, circular, without frames, twice as broad as the bars, of variable size. Bristles five to six times as long as one pore. Radial main-spines numerous, straight, slender, cylindrical, about as long as the diameter of the shell.

Dimensions.—Diameter of the shell 0.25 to 0.3, of the pores 0.012 to 0.02.

Habitat.—Tropical Atlantic, Stations 346 to 349, surface.

4. Castanidium murrayi, n. sp. (Pl. 113, figs. 5, 5a).

Pores subregular, circular, without frames, three times as broad as the bars. Bristles three times as long as one pore. Radial main-spines cylindrical, stout, irregularly curved, longer than the shell-diameter, covered with longish hexagonal dimples, which are separated by a network of prominent crests (fig. 5a).

Dimensions.—Diameter of the shell 0.4 to 0.5, of the pores 0.02 to 0.025.

Habitat.—North Atlantic, Station 352 to 354, surface.

5. Castanidium aldrichi, n. sp.

Pores subregular, circular, without frames, of variable size, about as broad as the bars. Bristles four times as long as one pore. Radial main-spines conico-cylindrical, irregularly curved, straight, about as long as the radius. (The conical base of the spines is inflated and fenestrated, therefore the shell is nearly polyhedral.)

Dimensions.—Diameter of the shell 0.35 to 0.4, of the pores 0.012 to 0.015.

Habitat.—Central Pacific, Stations 270 to 274, surface.

6. Castanidium bromleyi, n. sp.

Pores irregular, roundish, two to four times as broad as the bars. Bristles half as long as the radius. Radial main-spines cylindrical, straight, slender, longer than the shell-diameter.

Dimensions.—Diameter of the shell 0.22 to 0.26, of the pores 0.006 to 0.02.

Habitat.—Indian Ocean and Southern Pacific, Stations 162 to 169, surface.

7. Castanidium bethelli, n. sp.

Pores irregular, roundish or polygonal, two to three times as broad as the bars. Bristles one-third as long as the radius. Radial main-spines conico-cylindrical, irregularly curved, with dimpled surface, somewhat longer than the radius.

Dimensions.—Diameter of the shell 0.5 to 0.6, of the pores 0.015 to 0.03.

Habitat.—North Pacific, Stations 235 to 245, surface.

8. Castanidium moseleyi, n. sp. (Pl. 113, fig. 2).

Pores irregular, roundish or polygonal, two to four times as broad as the bars. Bristles about as long as the diameter of one pore, or a little longer. Radial main-spines cylindrical, irregularly curved, somewhat longer than the diameter of the shell; their base is more or less inflated and fenestrated, therefore the shell is nearly polyhedral.

Dimensions.—Diameter of the shell 0.7 to 0.8, of the pores 0.01 to 0.04.

Habitat.—Tropical Atlantic, Stations 346 to 349, surface.

Genus 708. Castanissa,^[325] Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 5.

Definition.—Castanellida with simple radial main-spines and a dentate mouth.

The genus Castanissa agrees with the preceding Castanidium in the possession of large radial main-spines, scattered between the numerous bristles or by-spines of the surface; but it differs from it in the possession of teeth around the mouth, identical with those of Castanella; it may be derived therefore either from the latter by development of main-spines, or from the former by formation of teeth.

1. Castanissa challengeri, n. sp. (Pl. 113, fig. 1).

Pores regular, circular, three times as broad as the bars. Bristles one-fourth as long as the radius. Radial main-spines (about twelve) very stout, straight, cylindrical, at the distal end conical, pointed, with dimpled surface, about half as long as the radius. Mouth very large, circular, about one-third as broad as the shell, with a corona of twelve to sixteen very large, triangular, parallel teeth.

Dimensions.—Diameter of the shell 0.7 to 0.8, of the pores 0.03.

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

2. Castanissa pearceyi, n. sp.

Pores regular, circular, twice as broad as the bars. Bristles half as long as the radius. Radial main-spines (about twenty) slender, cylindrical, smooth, irregularly curved, about as long as the radius. Mouth large, half as broad as the radius, with a corona of ten to twelve irregular, slender teeth.

Dimensions.—Diameter of the shell 0.5 to 0.6, of the pores 0.02.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.