Family LXXI. Phæodinida, Haeckel (Pl. 101, figs. 1, 2).

Definition.—Phæodaria without skeleton. Central capsule with one to three (or more) openings, placed in the centre of the spherical naked calymma.

The family Phæodinida is the simplest and most primitive of the Phæodaria, and differs from all the other families of this legion in the complete absence of a skeleton. It bears, therefore, the same relation to the latter as the Thalassicollida do to the other Spumellaria. The soft body is only composed of the central capsule with the nucleus, and the calymma with the phæodium.

Of course it is quite possible that the skeletonless Phæodaria, which we regard here as the ancestral family of that legion, may be either members of other families which have lost their skeleton accidentally, or young Phæodaria which have not yet developed a skeleton. But in some preparations of the Challenger certain large, well-preserved Phæodaria, without any trace of skeleton, are not rare; and since I myself have observed a complete living Phæodina, I have no doubt that they are independent, primordial forms (like Actissa, Thalassicolla, Cystidium, Nassella, &c.). Probably also two skeletonless Phæodaria belong to this family which are figured by R. Hertwig, in 1879, in his Organismus d. Radiol. (Taf. x. fig. 1, 11); this author, however, supposed that they had lost their original skeleton.

The three species of Phæodinida which are described in the sequel represent two different genera, Phæodina and Phæocolla, already distinguished in my first note on the Phæodaria (Sitzungsb. med.-nat. Gesellsch. Jena, 1879, Dec. 12, p. 4). Phæodina is a true Tripylea, and has the usual three openings which occur in the majority of Phæodaria, a large astropyle or main-opening on the oral pole of the main axis, and a pair of lateral accessory openings, or parapylæ, on the aboral pole. Phæocolla, however, has only a single opening, the astropyle, and agrees therefore with those Phæodaria which possess no parapylæ (Challengerida, Medusettida, Castanellida, &c.).

The complete body is in all observed Phæodinida a small jelly sphere of 1 to 3 mm. in diameter, with a transparent cortical layer and an opaque dark central part. This latter is the phæodium, in which the central capsule is hidden, surrounded on all sides by the gelatinous spherical calymma; the smooth surface of the latter is spherical.

The central capsule of the Phæodinida (Pl. 101, figs. 1, 2), is either spherical or spheroidal, somewhat lenticular, slightly depressed in the direction of the main axis. Its diameter is between 0.15 and 0.25. Its double membrane exhibits the same structure as in the other Phæodaria. The thick, double-contoured outer membrane is separated from the thin and delicate inner membrane by a clear space, filled up by jelly or by a fluid; the two are connected in Phæocolla (fig. 1) only at the astropyle, in Phæodina (fig. 2), they are also connected at the two parapylæ. The radiate operculum of the astropyle opens by a tubular prolongation or proboscis, which is very long in the former, shorter in the latter. The two parapylæ of the latter also bear short tubules. The protoplasm, enclosed in the inner membrane, contains numerous small circular vacuoles. The large central nucleus is sometimes spherical or ellipsoidal, at other times spheroidal or lenticular; it always contains numerous nucleoli. One specimen observed, with two nuclei, was apparently engaged in self-division (fig. 2).

The spherical gelatinous calymma, in the centre of which the central capsule is placed, has a diameter of 1 to 2 mm. In the specimen of Phæodina tripylea, which I observed living, it exhibited exactly the same shape as the figure of Dictyocha stapedia in Pl. 101, fig. 10; the only distinction in this latter being indicated by the pileated pieces of the skeleton on the surface. The jelly-sphere contained numerous roundish or globular alveoles of very different sizes, and between them an areolated network of protoplasm; the latter has arisen from the outer surface of the calymma in the form of very numerous, radiating, partly branched and anastomosing pseudopodia. The dark and opaque centre of the jelly-sphere is filled up by the granular, blackish-brown phæodium, which envelops the oral half of the central capsule completely; it exhibits the same characters as in all the other Phæodaria.

Synopsis of the Genera of Phæodinida.

Genus 656. Phæocolla,^[274] Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 4.

Definition.—Phæodinida with a single aperture to the central capsule (an astropyle with radiate operculum, placed on the oral pole of the main axis).

The genus Phæocolla may be regarded as the simplest form of all Phæodaria, and perhaps as the common ancestral form of this legion. It has no skeleton, and the central capsule exhibits only a single aperture on one pole of the main axis. In this it agrees with the Challengerida, Medusettida, and Castanellida, which have also no parapylæ or secondary openings.

1. Phæocolla primordialis, n. sp. (Pl. 101, fig. 1).

Central capsule subspherical, or somewhat depressed in the direction of the main axis. The oral pole of the latter exhibits a large astropyle, or a radiate operculum, about as broad as the nucleus. From its centre arises a conical mammilla, prolonged into a thin, cylindrical, S-like tubulus, the proboscis, which is about as long as the diameter of the capsule. The outer membrane of the capsule is thick and double-contoured; the inner is very thin, but distinct, and includes finely granulated protoplasm, and numerous spherical, clear vacuoles, each with some small granules. Nucleus spheroidal, depressed in the direction of the main axis, containing numerous dark, irregularly amœbiform nucleoli. The diameter of the nucleus is about equal to the radius of the central capsule. The extracapsular calymma is an alveolated sphere, the diameter of which is six to eight times that of the capsule. The inner part of it contains an irregular, blackish phæodium, which surrounds and hides the oral half of the central capsule.

Dimensions.—Diameter of the central capsule 0.16, of the nucleus 0.08, of the calymma 1.0 to 1.2.

Habitat.—Central Pacific, Station 271 to 274, surface.

Genus 657. Phæodina,^[275] Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 4.

Definition.—Phæodinida with three apertures to the central capsule (an astropyle on the oral pole of the main axis, and two lateral parapylæ on both sides of the aboral pole).

The genus Phæodina has the same structure of the central capsule as the majority of Phæodaria; one large main-opening or astropyle on the oral pole of the main axis, and two smaller lateral accessory openings or parapylæ on each side of the aboral pole: it is therefore a true Tripylean genus, like the majority of Phæodaria.

1. Phæodina tripylea, Haeckel (Pl. 101, fig. 2).

Central capsule spheroidal or lenticular, somewhat depressed in the direction of the main axis. Astropyle with a strongly ribbed, radiate operculum, scarcely one-third as broad as the diameter of the capsule, and prolonged into a short tubular proboscis. Parapylæ also with short tubular openings. The outer strong (double-contoured) membrane of the central capsule is separated from the inner thin (simple-contoured) membrane by a wide interval, filled up by a clear fluid or jelly; only at the three apertures both membranes are in direct connection. The granulated protoplasm contains numerous vacuoles, and surrounds a large spheroidal nucleus, with numerous small nucleoli. The voluminous calymma in a specimen, observed living, was alveolar, and the ramification of the pseudopodia, as well as the formation of the dark brown phæodium, very similar to that of Dictyocha stapedia (Pl. 101, fig. 10). Another specimen, figured in Pl. 101, fig. 2, exhibited the first stages of self-division; the reticulated nucleus and the radiate operculum of the astropyle were already doubled, and the two membranes of the capsule between them constricted in the median plane. To this species belong probably the central capsules figured by R. Hertwig, loc. cit.

Dimensions.—Diameter of the central capsule 0.15 to 0.25, of the nucleus 0.06 to 0.1, of the calymma 0.8 to 1.2.

Habitat.—Mediterranean; Portofino, near Genoa (Haeckel); Messina (Hertwig).

2. Phæodina cannopylea, n. sp.

Central capsule subspherical, scarcely depressed in the direction of the main axis. Astropyle with a finely ribbed radiate operculum, about as broad as the radius of the capsule, prolonged into a slender, tubular proboscis which is S-shaped, about as long as the radius, and similar to that of Phæocolla primordialis, Pl. 101, fig. 1. Parapylæ also tubular, with two slender prolongations, half as long and broad as the proboscis of the parapyle. Nucleus spheroidal, about half as broad as the capsule. This species differs from the preceding mainly in the cylindrical slender prolongations of the three apertures, which are similar to those of Aulosphæra and Aularia (Pl. 111, fig. 2).

Dimensions.—Diameter of the central capsule 0.2, of the nucleus 0.1, of the calymma 1.2 to 1.5.

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

Family LXXII. Cannorrhaphida, Haeckel, 1879 (Pl. 101, figs. 3-14; Pl. 114, figs. 7-13).

Definition.—Phæodaria with an incomplete skeleton, composed of numerous separate, not radially arranged pieces, which are either hollow tangential spicula or cap-shaped dishes, or fenestrated rings, scattered loosely in the calymma. Central capsule placed in the centre of the spherical calymma.

The family Cannorrhaphida comprises those Phæodaria in which the incomplete skeleton is represented by numerous separate pieces of silica, which exhibit very different forms, and are scattered tangentially on the surface of the spherical calymma, sometimes also throughout its jelly-mass. They agree in this peculiar character with the Thalassosphærida (among the Spumellaria) and bear the same relation to the skeletonless Phæodinida as the Thalassosphærida do to the Thalassicollida (compare pp. 10 and 29). The Cannorrhaphida represent the former group among the Phæodaria. They differ from the following family, the Aulacanthida, in the arrangement and position of the hollow spicula, which are never directed radially and never touch the central capsule, as is constantly the case in the latter.

Two genera of Cannorrhaphida have been hitherto known. The first species observed in a complete and living state (at Messina in 1859) was Cannobelos cavispicula, described in 1862 in my Monograph as Thalassoplancta cavispicula (loc. cit., p. 261, Taf. iii. figs. 10-13). I there figured a complete living specimen with expanded pseudopodia and a double central capsule (in the stage of self-division). The latter was surrounded by an alveolar calymma and by a voluminous mass of blackish-brown pigment, the phæodium; numerous, long, hollow, cylindrical tubes were scattered on the surface of the calymma. At that time I did not know the tripylean character of the central capsule and the peculiar radiate operculum in the Phæodaria, and therefore placed Thalassoplancta cavispicula among the Thalassosphærida.

The second description of a complete form of Cannorrhaphida was given in 1879 by R. Hertwig, under the name Dictyocha fibula (Organismus d. Radiol., p. 89, Taf. ix. fig. 5). The genus Dictyocha had been already founded by Ehrenberg in 1838, with the following definition:—"Lorica simplex, univalvis, silicea, laxe reticulata aut stellata" (Abhandl. d. k. Akad. d. Wiss. Berlin, 1838, p. 128). Ehrenberg had found only scattered pieces of the skeleton, fossil in Tertiary rocks. He placed them among the Bacillaria (= Diatomaceæ), but added, that they may be possibly scattered spicula of Sponges ("forsan Spongiarum ossicula").

In 1859 I myself observed similar forms of Dictyocha at Messina, and first recognised them as true Radiolaria. But I placed them at that time among the Acanthodesmida, beside Prismatium, supposing that a small spherical body which I had sometimes seen in the cavity of the pileated pieces (probably a phæodellum) was the small central capsule (Monogr. d. Radiol., 1862, p. 271, Taf. xii. figs. 3-6). The complete body of Dictyocha was not described till 1879, when R. Hertwig gave a full description of its peculiar structure, and especially of the great central capsule, which resembles that of the other Phæodaria. He first stated that the singular pileated pieces described by Ehrenberg were not complete shells, but isolated pieces of the skeleton, which are scattered in the jelly-envelope around the central capsule in a mode similar to the spicula of Thalassoplancta, Thalassosphæra and Sphærozoum. Hertwig also first recognised that the thin rods, which compose the reticular pileated pieces of the skeleton in Dictyocha, are not solid bars, but thin hollow tubules, similar to the hollow rods of Aulacantha and of other Phæodaria.

Numerous complete and well-preserved specimens of Dictyocha, which I found in the collection of the Challenger, have convinced me that the accurate description of R. Hertwig is correct in every respect, and that these remarkable bodies are true Phæodaria, most closely allied to Cannobelos (= Thalassoplancta) and to Aulacantha (compare Pl. 101, fig. 10). I now regard them as representatives of a peculiar subfamily of Cannorrhaphida, which I call Dictyochida. To the same subfamily also belong the small annular bodies which Ehrenberg described in 1841 as Mesocena (loc. cit., p. 401), and the elegant, more complicated, reticular and pileated bodies, which Stöhr figured in 1880 under the name Distephanus (Palæontogr., vol. xxvi. p. 121). These peculiar bodies are also only isolated pieces of the siliceous skeleton, and are scattered tangentially in great numbers in the calymma, around the tripylean central capsule. A still higher degree of development is attained by the interesting forms which I describe here as Cannopilus (Pl. 114, figs. 7-13). All these peculiar forms may be derived from the simple annular pieces of skeleton, which are aggregated in great numbers in the calymma of Mesocena. The pieces of the skeleton of these Dictyochida never assume the form of slender, cylindrical, tangential tubules which is characteristic of the Cannobelida.

A third subfamily of Cannorrhaphida, the Catinulida, is represented by the remarkable new genus Catinulus (Pl. 117, fig. 8). The single pieces of the skeleton, scattered in hundreds or thousands throughout the calymma, are here not composed of hollow rods, as in the two former subfamilies, but are solid hemispherical caps, or small, more flatly vaulted dishes, with a peculiar radial striation. All the complete specimens of Catinulus which I could examine possessed four equal central capsules, united in one spherical calymma.

The common character which unites the three rather different subfamilies, the Cannobelida, Dictyochida and Catinulida into a single family, and which separates this family, the Cannorrhaphida, from the other Phæodaria, is to be found in the composition of the rudimentary skeleton from numerous single pieces, which are loosely scattered either on the surface of the calymma, or throughout its jelly-mass, and which are never arranged radially and never touch the central capsule as is always the case in the closely allied Aulacanthida.

The slender spicula of the Cannobelida are cylindrical or spindle-shaped, tubular, scattered in variable numbers, but always in a tangential direction on the surface of the calymma. Usually they are 0.2 to 0.5 long, and 0.005 to 0.03 broad; either straight or slightly curved; smooth and simple in Cannobelos, spiny or branched in Cannorrhaphis (Pl. 101, figs. 3-5). Their wall is thin and fragile, their diameter sometimes equal throughout their whole length, at other times tapering towards both ends. Their cavity is filled by jelly, and seems to be open at both ends, since the purified and dried spicula constantly become filled by air.

The peculiar pieces of silica which compose the skeleton of the Catinulida are not hollow, like the rods of the other Cannorrhaphida, but concave hemispherical cups or more flatly vaulted little dishes, the thin flinty wall of which is slightly thickened at the circular margin, and radially striped above it. In all three species of Catinulus observed they were scattered throughout the calymma in hundreds or thousands (Pl. 117, fig. 8). Their relation to the Dictyochida is doubtful. Perhaps the small cups of Catinulus may be derived from the simple rings of Mesocena, by development of an operculum on one side of the ring.

The skeleton of the Dictyochida is much more developed and possesses a higher morphological interest; the numerous different forms, however, which its pieces here assume, may be all derived from the simple circular ring of Mesocena. This ring is formed by a thin, hollow, cylindrical, or prismatic rod, sometimes circular or elliptical, at other times polygonal. From its margin small, hollow, radial spines often proceed (Pl. 101, fig. 9). In Dictyocha there arise from the ring two, three, four or more siliceous bars or arches, which form one or more bulges over one side of the ring; usually the little fenestrated shell thus produced assumes the form of a three-sided or four-sided pyramid, or of a little hat with three or four meshes (Pl. 101, figs. 10-14). From this Dictyocha (in a restricted sense) we separate the genus Distephanus, in which the little pyramids become truncated, so that one central apical mesh (the apical or upper ring) is surrounded by four, five, six or eight lateral meshes, the sides of the pyramid (Pl. 114, figs. 7-9). The edges of the small pyramid are formed by the same number of siliceous bars arising from the ring and alternating with the meshes. Radial spines in different numbers and arrangements arise from the corners of the two parallel rings, as well from the smaller apical as from the larger basal ring. The simple apical ring of Distephanus becomes divided or fenestrated in the highest developed genus of this subfamily, in Cannopilus (Pl. 114, figs. 10-13); each pileated piece of the skeleton exhibits here two rows of alternating lateral meshes, an upper row of smaller and a lower row of larger meshes.

The majority of Dictyochida are armed with spines or thorns, which arise in a regular manner from different points of the annular or pileated pieces. In the ancestral genus, Mesocena, radial spines start from the corners of the simple ring in centrifugal direction, and lie horizontally in its plane. As these primary corner-spines determine the radial composition of the more highly developed genera we call them perradial (lying in rays of the first order). In Dictyocha and Distephanus commonly (but not quite constantly) these perradial spines alternate with the ascending bars which bisect the sides of the basal ring; these bars are therefore interradial (lying in rays of the second order); consequently also the corners of the apical ring of Distephanus are interradial. The latter also often bear small thorns or teeth. Other teeth frequently start in centripetal direction from the lower or basal ring, on the side of the perradial spines, and frequently they are directed obliquely downwards.

In Dictyocha and Distephanus are frequently found remarkable twin pieces, composed of two pileated and reticulated skeleton pieces. These are united by their basal rings loosely in such a way that they form together a small fenestrated subspherical body; the union is strengthened by those small teeth of the basal rings, which are directed downwards and catch one into the other (Pl. 101, fig. 12; Pl. 114, fig. 8). A similar twin piece has been already observed by Stöhr in the fossil Distephanus rotundus, and upon this was founded this genus. Since the teeth of the two opposed basal rings, catching one into the other, seem to be specially adapted for the composition of those small double pyramids, it is probable that the latter possess a special protective function in these Phæodaria, and perhaps envelop their phæodella or their flagellate spores (?). In every case these formations are very remarkable.

The Central Capsule of the Cannorrhaphida seems to possess the same shape in the three subfamilies, and to agree in general with that of the Aulacanthida. In a living specimen of Dictyocha stapedia, which I observed at Ceylon (Pl. 101, fig. 10), the three openings of the Tripylea were distinct; the radiate operculum of the astropyle (on the oral pole) was surrounded by the granules of the dark phæodium, whilst on the opposite aboral side, two parapylæ or conical secondary openings were visible. The voluminous spherical calymma (about four times as broad as the central capsule) contained numerous large alveoles (as in Aulosphæra) and its surface was protected by numerous pileated pieces of the skeleton; the basal ring of the latter was placed tangentially in the spherical surface of the calymma, their apical spine being directed outwards. The pseudopodia, arising from the central capsule and forming a network between the alveoles of the calymma, radiated outwards in great number from its surface (Pl. 101, fig. 10).

The propagation by self-division seems to be very frequent in the Cannorrhaphida. I frequently found two equal central capsules in one calymma, as in the first observed species, Cannobelos cavispicula, and in Cannorrhaphis spinulosa (Pl. 101, fig. 3), sometimes also in Dictyocha and Distephanus. As already mentioned, Catinulus constantly exhibited four central capsules united in each calymma.

Synopsis of the Genera of Cannorrhaphida.

Subfamily 1. Cannobelida, Haeckel.

Definition.—Cannorrhaphida with numerous hollow cylindrical or spindle-shaped tubes, which lie tangentially scattered on the surface of the spherical calymma.

Genus 658. Cannobelos,^[276] n. gen.

Definition.—Cannorrhaphida with a skeleton composed of tubular acicular pieces, which are smooth, cylindrical or spindle-shaped tangential needles, without spines and branches.

The genus Cannobelos, and the following closely allied Cannorrhaphis, represent the peculiar subfamily Cannobelida, differing from the other Cannorrhaphida in the acicular form of the pieces of the skeleton, which are tangentially scattered on the surface of the spherical calymma. The cylindrical or spindle-shaped hollow needles are smooth in Cannobelos, whilst in Cannorrhaphis they are studded with lateral spines or branches.

1. Cannobelos cavispicula, Haeckel.

Tangential tubes cylindrical, more or less curved, gradually tapering towards the two pointed ends. Calymma with a voluminous phæodium.

Dimensions.—Length of the tubular spicule 0.25, breadth 0.003.

Habitat.—Mediterranean, Messina, surface.

2. Cannobelos calymmata, n. sp.

Tangential tubes cylindrical, straight, of equal breadth throughout their whole length, closed by a hemispherical cap on the two rounded ends. Calymma very voluminous, with a small phæodium.

Dimensions.—Length of the tubular spicula 0.3 to 0.5, breadth 0.004 to 0.008.

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

3. Cannobelos thalassoplancta, n. sp.

Tangential tubes spindle-shaped, straight, gradually tapering towards the two pointed ends. Calymma and the included phæodium rather voluminous.

Dimensions.—Length of the tubular spicula 0.15 to 0.2, breadth in the middle part 0.02.

Habitat.—Tropical Atlantic, Station 347, surface.

Genus 659. Cannorrhaphis,^[277] Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 4.

Definition.—Cannorrhaphida with a skeleton composed of tubular acicular pieces, which are spiny, cylindrical or spindle-shaped tangential needles, either with lateral spines or branches.

The genus Cannorrhaphis differs from the preceding closely allied Cannobelos in the spiny shape of the tangential acicular spicula, which are studded either with short spines or with longer lateral branches.

1. Cannorrhaphis spinulosa, n. sp. (Pl. 101, figs. 3, 4).

Tangential tubes cylindrical, straight, gradually tapering towards the two pointed ends, densely studded with conical spines, arising perpendicularly. (The specimen figured, fig. 3, exhibited two ovate central capsules, each of which contained two large nuclei, with numerous nucleoli.)

Dimensions.—Length of the tubular spicula 0.3 to 0.5, breadth 0.01 to 0.015.

Habitat.—North Pacific, Station 244, surface.

2. Cannorrhaphis lampoxanthium, n. sp.

Tangential tubes cylindrical, more or less curved, suddenly tapering towards the two pointed ends, densely studded with irregular conical spines of unequal length, which arise obliquely from their surface.

Dimensions.—Length of the tubular spicula 0.4 to 0.5, breadth 0.005 to 0.008.

Habitat.—South Pacific, Station 289, depth 2550 fathoms.

3. Cannorrhaphis lappacea, n. sp.

Tangential tubes spindle-shaped, gradually tapering towards the two pointed ends, densely studded with irregular lateral branches, which are partly simply, partly forked, more or less curved, and arise obliquely from their surface.

Dimensions.—Length of the tubular spicula 0.2 to 0.3, breadth 0.015 to 0.025.

Habitat.—Central Pacific, Station 271, surface.

4. Cannorrhaphis spathillata, n. sp. (Pl. 101, fig. 5).

Tangential tubes cylindrical, thin and straight, regularly zigzag, with pointed, regularly alternating lateral spines, with an elegant spathilla, or a cap-shaped verticil of eight to ten recurved spines on the two ends.

Dimensions.—Length of the tubular spicula 0.3, breadth 0.003.

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

Subfamily 2. Catinulida, Haeckel.

Definition.—Cannorrhaphida with a skeleton composed of numerous cap-shaped pieces, which lie tangentially scattered on the surface of the spherical calymma. Each piece is a hemispherical or flatly cap-shaped siliceous body, often with radial striations, and with a thin solid wall.

Genus 660. Catinulus,^[278] n. gen.

Definition.—Cannorrhaphida with a skeleton composed of solid, cap-shaped or hemispherical, not fenestrated, pieces.

The genus Catinulus differs from all the other Cannorrhaphida in the peculiar shape of the numerous siliceous pieces, which are scattered on the surface of the calymma and compose their rudimentary skeleton. These pieces are neither hollow rings (as in the Dictyochida), nor hollow tubes (as in the Cannobelida), but solid hemispherical caps or more flatly vaulted small dishes. All the complete specimens of this genus which I observed exhibited four equal central capsules in the spherical calymma.

1. Catinulus quadrifidus, n. sp. (Pl. 117, figs. 8, 8a).

Cap-shaped pieces of the skeleton flatly vaulted, three times as broad as high, smooth; the marginal ring with fine radial ribs and with smooth margin.

Dimensions.—Diameter of the calymma 0.6 to 0.8, of the four central capsules 0.12 to 0.2; breadth of the concave caps 0.024, height 0.008.

Habitat.—South Atlantic, Station 323, depth 1900 fathoms.

2. Catinulus catillum, n. sp.

Cap-shaped pieces of the skeleton flatly vaulted, three times as broad as high, rough, covered with numerous small spinules; the marginal ring with stout radial ribs and a corona of denticles on the margin.

Dimensions.—Breadth of the concave caps 0.03, height 0.01.

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

3. Catinulus lopadium, n. sp.

Cap-shaped pieces of the skeleton hemispherical, twice as broad as high, smooth; the marginal ring smooth, slightly radiate, with thickened smooth margin.

Dimensions.—Diameter of the calymma 1.2, of the central capsule 0.22; breadth of the concave caps 0.024, height 0.012.

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

Subfamily 3. Dictyochida, Haeckel.

Definition.—Cannorrhaphida with a skeleton composed of numerous annular pieces, which lie tangentially scattered on the surface of the calymma. Each piece is either a simple hollow ring or a pileate and reticulate cap, composed of a ring and several connected bars.

Genus 661. Mesocena,^[279] Ehrenberg, 1841, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 401.

Definition.—Cannorrhaphida with a skeleton composed of simple annular pieces, each of which is a circular, elliptical or polygonal, not fenestrated, ring, with or without radial spines.

The genus Mesocena is the simplest form of the Dictyochida, and no doubt the common ancestral form of this subfamily. The siliceous pieces, which are scattered in variable and indefinite number in the calymma, are simple hollow rings, with or without spines on the periphery. Ehrenberg, who first described and figured such rings (found fossil in different Tertiary rocks) has mistaken them for Diatoms. Some species, which I found in the Challenger preparations, leave no doubt that these rings are the siliceous pieces of the skeleton of the simplest Dictyochida. They are scattered in great numbers in the spherical calymma, which surrounds a tripylean central capsule with all the characters of the Phæodaria. In the living body the rings probably always lie in the spherical periphery of the extracapsular jelly-veil, in tangential planes, whilst in some of the Challenger preparations the rings were scattered in hundreds throughout the whole jelly-mass. In a few species the rings are quite simple, circular or elliptical, smooth, and without teeth or spines. In the majority of species some teeth or radial spines, regularly disposed, arise from the periphery of each ring (two, three, four to eight; sometimes sixteen, eight smaller alternating with eight larger spines). In some species small teeth occur on the inner margin of the rings. The number of radial spines seems to be rather constant in all the rings of one and the same individual, with the exception of a few variations. Thus in Mesocena octogona I found here and there single rings with seven or nine teeth, instead of the usual number eight. Ehrenberg enumerated sixteen different species of Mesocena; many, however, of these are synonymous, being founded on slight variations in the number of the teeth; of others he has given only the name, but neither a figure nor a description (e.g., Mesocena stephanolithis, Mesocena spongolithis, &c.).