The genus Cœlodoras is the simplest form of the Cœlodendrida, and may be regarded as the common ancestral form of this and of the following family. It differs from all other members of these two families in the simple shape of the hollow radial tubes which arise from the galea, and are neither branched nor forked; the galea is very small, a flat triangular cap. Cœlodoras may be derived immediately from Concharium or Conchonia (p. 1723), by development of the galea and the radial tubes.

1. Cœlodoras hexagraphis, n. sp.

Three straight, cylindrical, equidistant hollow tubes arise divergent from the three corners of each galea, and are about as long as the diameter of the valves, at the distal end armed with a spinulate knob. The odd sagittal (or caudal tube) is directed backwards, the two paired (or pectoral) tubes, forwards.

Dimensions.—Diameter of the valves 0.16, length of the tubes 0.2.

Habitat.—Central Pacific, Station 266, depth 2750 fathoms.

2. Cœlodoras octographis, n. sp.

Four hollow cylindrical tubes, slightly curved, arise divergent from each galea, and are about one and a half times as long as the diameter of the valves, at the distal end knob-shaped, and armed with four crossed, recurved teeth. Two anterior (or pectoral) tubes arise from the two frontal corners of the galea basis, and diverge forwards to right and left. Two posterior tubes (a sagittal and a caudal) arise from the posterior corner of each galea, and diverge in the sagittal plane backwards.

Dimensions.—Diameter of the valves 0.2, length of the tubes 0.3.

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

Genus 728. Cœlodendrum,^[344] Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 801.

Definition.—Cœlodendrida without external lattice-mantle, with branched radial tubes, the hollow branches of which are free and never connected by anastomoses.

The genus Cœlodendrum is the first described form not only of the family Cœlodendrida, but of all Phæoconchia or bivalved Phæodaria; it is also the most common form of this group, and represented by ten different species, some of which are cosmopolitan, very common, and widely distributed. In my first description of Cœlodendrum I confounded it erroneously with some forms of Cœlodasea and Cœlographis, the separated fragments of which I had found entangled between the branches of the former. The first figures of Cœlodendrum are given in my Monograph, in 1862, Taf. xiii. figs. 1-3 (not 4) and Taf. xxxii. fig. 1 (not 2 and 3). Cœlodendrum has been derived from Cœlodoras by furcation and repeated dichotomous ramification of the hollow radial tubes which arise from the galea.

Subgenus 1. Cœlodendridium, Haeckel.

Definition.—Ramification of the hollow tubes regularly dichotomous, each branch being forked again; therefore the two terminal ramules of the last branches equal.

1. Cœlodendrum ramosissimum, Haeckel.

Terminal branches regularly forked, with two equal, smooth, nearly straight or slightly curved fork-branches, diverging at right angles; their end-knobs with four crossed (or sometimes five or six) short recurved teeth.

Dimensions.—Diameter of the spherical skeleton 1.2 to 1.8, of the two central valves 0.2 to 0.25.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific; many Stations, surface and at various depths.

2. Cœlodendrum spinosissimum, n. sp. (Pl. 121, fig. 7).

Terminal branches regularly forked, with two equal, smooth, straight, fork-branches, diverging at right angles, their end-knobs echinoidal, subspherical or club-shaped, with numerous short radial thorns.

Dimensions.—Diameter of the skeleton 2 to 2.2, of the two central valves 0.25 to 0.03.

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

3. Cœlodendrum furcatissimum, n. sp. (Pl. 121, fig. 1-4).

Terminal branches regularly forked, with two equal, smooth, straight, or slightly curved fork-branches, diverging at acute angles; their end-knobs very small, with three short, diverging, conical teeth.

Dimensions.—Diameter of the skeleton 2 to 2.5, of the two central valves 0.3 to 0.4.

Habitat.—Cosmopolitan; Atlantic, Indian, Pacific; many Stations, surface, and at various depths.

4. Cœlodendrum bifurcum, n. sp.

Terminal branches regularly forked, with two equal, smooth, more or less curved fork-branches, diverging at acute angles; their end-knobs thin, with two slender, parallel, bristle-shaped teeth.

Dimensions.—Diameter of the skeleton 0.6 to 0.8, of the two central valves 0.1 to 0.15.

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

5. Cœlodendrum gracillimum, Haeckel.

Terminal branches regularly forked, with two equal, spinulate, curved fork-branches, diverging at obtuse angles and covered with numerous small thorns; their end-knobs cap-shaped, with a corona of six to eight small recurved teeth. In one specimen of this species (in 1859) I found entangled the fragments of Cœlographis gracillima, figured in Taf. xxxii. figs. 2, 3, loc. cit. I supposed at that time, erroneously, that the latter belonged to full-grown specimens of the former.

Dimensions.—Diameter of the skeleton 1 to 1.2, of the valves 0.15 to 0.2.

Habitat.—Mediterranean (Messina), surface.

6. Cœlodendrum lappaceum, n. sp.

Terminal branches regularly forked, with two equal, spinulate, straight or slightly curved fork-branches, diverging at acute angles and covered with small recurved hooks; their end-knobs large, conical, with a prominent apex and a basal corona of six to eight recurved teeth.

Dimensions.—Diameter of the skeleton 1.5 to 1.8, of the valves 0.22.

Habitat.—South Pacific, Stations 285 to 295, depth 1500 to 2600 fathoms.

Subgenus 2. Cœlodendronium, Haeckel.

Definition.—Ramification of the hollow tubes more or less irregular, mainly in the periphery; the terminal ramules of the last branches unequal.

7. Cœlodendrum cervicorne, n. sp. (Pl. 121, fig. 8).

Terminal branches irregularly ramified, with unequal, smooth, curved ramules, diverging at obtuse angles, their end-knobs echinoidal, small, with short, diverging, conical thorns.

Dimensions.—Diameter of the skeleton 1 to 1.2, of the valves 0.2.

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

8. Cœlodendrum digitatum, n. sp.

Terminal branches irregularly ramified, with unequal, spinulate, straight ramules, diverging at acute angles; the two last fork-branches digitate, each with five diverging finger-shaped ramules, lying in a meridian plane; their end-knobs conical, pointed, with a corona of recurved hooks.

Dimensions.—Diameter of the skeleton 1.6, of the valves 0.24.

Habitat.—Indian Ocean, Madagascar (Rabbe), surface.

9. Cœlodendrum flabellatum, n. sp. (Pl. 121, fig. 6).

Terminal branches flabellate, irregularly ramified, each of the last two fork-branches being divided into four or five diverging straight branches of different lengths; usually the last eight or ten ramules lie in a meridional plane; their end-knobs cap-shaped, with a corona of recurved teeth.

Dimensions.—Diameter of the skeleton 2.0 to 2.5, of the valves 0.25 to 0.3.

Habitat.—North Pacific, Station 235 to 240, surface.

10. Cœlodendrum serratum, n. sp. (Pl. 121, fig. 5).

Terminal branches flabellate, irregularly ramified like the preceding species; it differs from this in the strong compression of the broad, saw-shaped, terminal branches; the two opposite edges (placed in the meridional plane of the flabellum) are finely serrated; their end-knobs with a corona of diverging teeth.

Dimensions.—Diameter of the skeleton 3.0 to 3.2, of the valves 0.3 to 0.36.

Habitat.—Central Pacific, Stations 270 to 274, depth 2350 to 2925 fathoms.

Subfamily 2. Cœlodrymida, Haeckel.

Definition.—Cœlodendrida with an external bivalved lattice-mantle, produced by the anastomosing branches of the hollow radial tubes.

Genus 729. Cœlodrymus,^[345] Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 6.

Definition.—Cœlodendrida with an external bivalved lattice-mantle, produced by the anastomosing terminal branches of the hollow tubes, which are connected in a spherical face.

The genus Cœlodrymus, and the following closely allied genus Cœlodasea, represent together the small subfamily Cœlodrymida, differing from the Cœlodorida in the possession of an outer bivalved lattice-mantle. They exhibit therefore the same relation to the latter, that in the following family the Cœloplegmida bear to the Cœlotholida. The bivalved spherical mantle is composed of a simple lattice-plate in Cœlodrymus, of a spongy framework in Cœlodasea; the anastomosing branches of the hollow radial tubes become connected in the former in a spherical face, in the latter in the form of a spongy framework.

1. Cœlodrymus ancoratus, n. sp. (Pl. 121, figs. 9, 10).

Network of the mantle loose, with large, irregular, polygonal meshes; the terminal branches of the forked trees, which communicate at the spherical surface of the calymma, and compose the mantle, are smooth. Spherical surface covered with very numerous and thin zigzag radial filaments, which are about as long as the galea, and bear at the distal end an anchor with two recurved teeth, denticulate at the concave proximal edge (fig. 10).

Dimensions.—Diameter of the spherical lattice-mantle 2 to 2.5, of the valves 0.3 to 0.4.

Habitat.—South-Eastern Pacific (off Juan Fernandez), Station 300, depth 1375 fathoms.

2. Cœlodrymus lappulatus, n. sp.

Network of the mantle rather dense, with numerous and small irregular polygonal meshes; the terminal branches of the forked trees, which compose the mantle, are spinulate. Spherical surface densely studded with very numerous spinulate, radial filaments, which are about half as long as the galea, and bear at the distal end an anchor with four crossed recurved teeth, denticulate at the concave proximal edge.

Dimensions.—Diameter of the spherical lattice-mantle 2.5 to 3, of the valves 0.4 to 0.5.

Habitat.—South-Western Pacific (east of New Zealand), Station 169, depth 700 fathoms.

3. Cœlodrymus echinatus, n. sp.

Network of the mantle very dense, with very numerous and small irregular roundish meshes; the terminal branches of the forked trees, which compose the mantle, are spiny. Spherical surface studded with very numerous, thin, radial bristles, which bear no anchor at the distal end.

Dimensions.—Diameter of the spherical lattice-mantle 1.8, of the valves 0.22.

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

Genus 730. Cœlodasea,^[346] n. gen.

Definition.—Cœlodendrida with an external spongy lattice-mantle, produced by the anastomosing branches of the hollow tubes, which are connected in different heights.

The genus Cœlodasea differs from the preceding Cœlodrymus in the spongy structure of the outer bivalved mantle. The hollow branches of the radial tubes of Cœlodendrum, which anastomose in Cœlodrymus only on the spherical surface of the calymma, and form a simple lattice-sphere, become connected in Cœlodasea in different planes (laterally and terminally), and therefore form an irregular spongy framework. The latter exhibits therefore to the former a relation similar to that which Spongoplegma bears to Carposphæra among the Sphæroidea.

1. Cœlodasea ramosissima, Haeckel.

Spongy framework of the spherical bivalved mantle very dense and thick, produced by very numerous, irregular anastomoses of the lateral and terminal branches, which arise from the hollow tubes. The last and thinnest terminal branches are forked, as seen in the radial section of fig. 4 (loc. cit.), their ends are closed and armed with some very small denticles (not open, as figured in fig. 4). In my Monograph I had confounded this species with Cœlodendrum ramosissimum, which however, may possibly be its ancestral form.

Dimensions.—Diameter of the spongy spherical mantle 2 to 2.5, of the central valves 0.15.

Habitat.—Mediterranean (Messina), surface.

2. Cœlodasea spongiosa, n. sp.

Spongy framework of the bivalved mantle rather loose, not nearly so thick and dense as in the preceding species. The last and thinnest terminal branches are prolonged into denticulate, zigzagged, radial filaments, which bear at their distal end an anchor with two recurved teeth (similar to Cœlodrymus ancoratus, Pl. 121, figs. 9, 10).

Dimensions.—Diameter of the spongy spherical mantle 3 to 3.2, of the central valves 0.24.

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

Family LXXXV. Cœlographida, n. fam. (Pls. 122, 126-128).

Definition.—Phæodaria with a bivalved lattice-shell, composed of two hemispherical valves, a dorsal and a ventral. A conical cupola or a helmet-shaped galea arises on the apical pole of each valve, therefore on the opposite poles of the sagittal axis. The cavity of the galea communicates with the sagittal rhinocanna, a peculiar nasal tube, which rests upon the valve, and is connected with the galea by a simple or double frenulum; its opening being directed towards the proboscis. Three or more branched hollow radial tubes arise from each valve, and are symmetrically disposed. Sometimes their branches form an outer bivalved mantle. The central capsule is so enclosed between the two inner valves, that its three openings lie in the open frontal fissure between them.

The family Cœlographida, the last family of the Phæodaria, exhibits the highest degree of morphological development, not only in this group, but among all Radiolaria. They attain also the greatest size of all members of the class, since the diameter of their body is sometimes more than 20 mm., and in a few species even more than 30 mm. The complexity of their structure attains at the same time such a high degree, that they may be regarded as the most complicated, and (in a morphological sense) as the most highly developed of all Protozoa. Nevertheless their body always remains a single cell, and is closely allied to the preceding Cœlodendrida; they differ from the latter mainly in the development of a peculiar new organ, the "rhinocanna," or "nasal tube." This is a hollow tube placed in the sagittal plane, arising from the base of each galea, and is connected with its apex by a simple or double frenulum. Between the oral openings of the two opposed rhinocannæ (one dorsal and one ventral) lies the proboscis of the central capsule.

The first observed species of Cœlographida was Cœlographis gracillima, some parts of which (but not the entire skeleton) were figured in my Monograph (1862, Taf. xxxii. figs. 2, 3). But I confounded these with Cœlodendrum gracillimum, in the branched hollow trees of which the fragments of the former were entangled. I detected this error afterwards, when I had the opportunity of the observing some complete specimens. The first description of a complete skeleton was given in 1882 by O. Bütschli, who examined a large specimen of Cœlothamnus davidoffii, captured by Davidoff in the Mediterranean (Zeitschr. f. wiss. Zool., Bd. xxxvi. p. 486, Taf. xxxi.). In the rich collection of the Challenger I was able to distinguish not less than nine genera and twenty-six species of Cœlographida, but the majority of their large and most fragile skeletons were more or less injured, or quite broken. It was, therefore, of the highest importance for the minute study of this difficult group, that Dr. John Murray, during his expedition to the Færöe Channel (in 1882, in H.M.S. "Triton"), discovered in the Gulf Stream the beautiful Cœloplegma murrayanum, and brought up home hundreds of well-preserved specimens (Pl. 127). Only by the complete examination of this excellent material it was possible to answer many difficult questions as to their morphology, and to correct the errors in my description and in that of Bütschli.

We divide the family Cœlographida into two rather different subfamilies, which may afterwards be separated as two divergent families, the Cœlotholida (Pl. 122) and Cœloplegmida (Pls. 126-128). Both groups may be easily distinguished at a glance, since the numerous branches, arising from the hollow radial tubes, remain constantly free and independent in the former, and represent a spiny thicket, whilst in the latter they constantly become united, and by anastomosing form a peculiar "mantle," or outer envelope of delicate network. But besides, there are other and more important differences between the two groups. The peculiar hollow tube, arising from the base of the galea on each valve, which is filled with phæodella, and which we call the rhinocanna, develops in the Cœlotholida on its open mouth two paired lateral frenula (right and left), which connect it (like two lateral bridges) with the base of two paired hollow main tubes (the "frontal tubes"). In the Cœlospathida, however, the mouth of the rhinocanna develops a single odd frenulum only (in the sagittal plane), and is connected by it with the base of an odd, single, hollow main tube, directed forwards, the "nasal style."

The central bivalve lattice-shell, from which the galea and the tubes arise, exhibits in the Cœlographida essentially the same form and structure as in the preceding Cœlodendrida. The only (but important) difference between them is indicated by the constant presence of the peculiar rhinocanna in the former, whilst this is always absent in the latter. The two valves of the shell, dorsal and ventral, are either hemispherical or somewhat flatter, sometimes nearly cap-shaped, and formed of an extremely delicate and irregularly fenestrated plate of silica, as in the Cœlodendrida. As in the latter, so also in the Cœlographida both valves are of similar form and usually of equal size, but sometimes the dorsal is a little smaller than the ventral valve. The remarkable difference which Bütschli describes in his Cœlothamnus davidoffii, and the inverse origin of the three tubes in both valves (loc. cit., Taf. xxxi; figs. 2, 4), depends upon an error of observation, produced by the artificial inversion of one valve, and the dislocation of their natural arrangement. The valves are never in direct contact, but separated by the equatorial fissure or girdle-cleft, in which the girdle zone of the enclosed central capsule and its three openings lie freely (Pl. 127, figs. 4, 5; Pl. 128, fig. 2). The free margins of both valves, which are opposite to one another, and bound the girdle-cleft, are always equidistant, so that the cleft in the whole equatorial circumference is of equal breadth. The margins are usually irregularly denticulate, sometimes armed with longer bristles (Pl. 127, fig. 8), more rarely smooth (fig. 5). The delicate lattice-work of the valves is always irregular and very variable, usually with numerous small and unequal pores, sometimes rudimentary, so that the valves appear partly solid and hyaline. The size of the valves is usually between 0.2 and 0.5 (in diameter).

The galea (g) or the apical cupola, which arises from the vaulted apex of each valve (or its sagittal pole) is more developed in the Cœlographida than in the preceding Cœlodendrida, and differs from the latter in the peculiar rhinocanna arising from its base, and in the single or double frenulum, connecting the open mouth of the rhinocanna with the odd or paired main tube arising from the galea. The two opposite galeæ lie therefore on the poles of the sagittal axis of the bivalve shell, and are so symmetrically disposed in the sagittal plane, that the open mouths of their rhinocannæ are directed towards the oral pole of the main axis, and nearly come in contact with the proboscis arising from the radiate operculum of the central capsule (Pl. 127, figs. 4, 5).

The size and form of the galea are very variable, even in one and the same species. The volume of its cavity is generally about as great as that of the hemispherical valve from which it arises, sometimes larger, at other times smaller. Its fundamental form is constantly dipleuric or bilateral, since the radial hollow tubes arise symmetrically on both its sides, and the rhinocanna proceeding from its base determines the sagittal plane. Usually the galea has the form of a vaulted helmet, the convex crest of which is inclined towards the mouth (Pl. 127, figs. 4, 5, 8, 9). Its anterior or apical part is broad and truncated in the Cœlotholida, more or less conical in the Cœlospathida; sometimes it assumes nearly the form of a bilateral three-sided pyramid, at other times it is more pear-shaped (Pls. 126-128). The thin siliceous wall of the galea has the same irregular and delicate network as the valve from which it arises, and sometimes the small irregular pores are also here reduced, so that the wall becomes partly solid. In some cases the thin, solid, siliceous plate of the galea and of the valve is covered by an irregular delicate network of crests; the dimples between these crests may be easily confounded with true pores.

The cavity of the galea is filled with phæodella and does not communicate with the cavity of the shell-valves, nor with the cavity of the radial tubes filled by jelly; it is closed towards the latter and the former by a thin solid plate of silex. Bütschli (1882, loc. cit., p. 488) describes in Cœlothamnus a large circular opening (Taf. xxxi. figs. 2a, 4a), and states that this is a direct communication between the cavities of the valves and of their galeas which are called by him "der dreiseitige kastenförmige Aufsatz" (ε). This error was caused by the fact that he observed the valves from the apical face only. The apparent opening of communication does not exist, and is the optical section of the rhinocanna, the shortened walls of which he describes as "trapezförmige Kiesellamelle" (γ); the two lateral edges of the latter ("die seitlichen Zipfel," δ) are the paired frenula, which connect the open mouth of the rhinocanna with the base of the two frontal tubes.

The "rhinocanna or nasal tube" (Pl. 126, figs. 1, 4; Pl. 127, figs. 4-9t) is a very remarkable organ which is common to all Cœlographida (without any exception), and distinguishes them markedly from all the other Radiolaria, and particularly from the closely allied Cœlodendrida in which we find no trace of it. The rhinocanna is a cylindrical or three-sided prismatic hollow tube, which lies in the sagittal plane, on the outer surface of each valve, arises from the base of the galea, and is directed towards the proboscis of the central capsule. The two opposite rhinocannæ open on each side of the latter (Pl. 127, figs. 4-9m), and usually this "nasal mouth" or the anterior opening of the nose is somewhat dilated or even funnel-shaped. The posterior opening of the nose passes directly over into the base of the cavity of the galea.

Usually the rhinocanna is densely filled up by dark phæodella, which enter by this channel into the cavity of the galea (Pl. 127, figs. 4, 5, 9). Sometimes the entire phæodium is enclosed in the two galeæ and their rhinocannæ (figs. 5, 9), whilst at other times a great part of the phæodium lies outside of their cavities, and surrounds the proboscis of the mouth, or even the anterior half of the central capsule (fig. 4). The length of the cylindrical rhinocanna is usually about equal to that of the galea, whilst the diameter of the latter is from three to five times as great as that of the former. The structure of the thin wall is the same in both. The fine reticulation (fig. 8) is produced either by true, very small and irregular pores, or by a fine network placed on the solid thin wall. We may distinguish on each rhinocanna an outer or distal convex face, which is opposite to the proximal concave face of the galea, and an inner concave or proximal face, which rests immediately upon the convex outer face of the shell-valve; a thin solid lamella of silica here completely separates the cavities of the valve and of the rhinocanna resting upon it.

The "frenula or nasal suspensoria" (Pl. 127, figs. 4-9b) are thin ligaments of silica, which connect the nasal mouth (m) with the base of the main tubes arising from the galea; they are, therefore, also common to all Cœlographida, and an exclusive and marked attribute of this family. They are, however, different in the two subfamilies of this group, corresponding to the different origin of the odd or paired main tubes. In the Cœloplegmida (Pls. 126-128) from the apex of each galea arises an odd main style, the nasal style (g 1), and its base is connected with the nasal mouth by an odd frenulum (b). In the Cœlotholida however (Pl. 122) the large nasal odd style is always wanting, and there arise two paired frontal tubes from the two corners of the truncate frontal face of the galea; therefore two paired frenula are developed (a right and a left), and these, converging towards the nasal mouth, connect its distal corner with the base of the two frontal tubes.

The odd frenulum of each valve of the Cœloplegmida lies therefore in the sagittal plane, whilst the two paired frenula of the Cœlotholida lie on both sides of it, to the right and left. The frenula seem to be supporting columellæ or pillars, which support the fragile skeleton, and mainly effect a fixed prop for the fragile galea. In the Cœlotholida the frenula are often rather broad and irregularly fenestrated lamellæ of silica (Pl. 122, fig. 2), whilst in the Cœloplegmida they are usually thin ligaments, fenestrated only at the broadened ends, which are inserted inside on the distal apex of the nasal mouth, and outside on the base of the nasal main styles.

The large hollow tubes which arise from the galea of all Cœlographida, are very variable in number, size and shape, but are always richly branched and symmetrically arranged in the dorsal and the ventral valve of the shell. They exhibit an important difference in the two subfamilies of the group; in the Cœlotholida all the branches, and also the thin terminal ramules, are free, without any junction; in the Cœloplegmida, however, they communicate by frequent anastomoses, and the connected terminal ramules form on the surface of the calymma an outer lattice-mantle of very delicate network. Another marked difference between the two families is indicated by the origin and site of those main tubes which are connected with the rhinocanna by a frenulum. In the Cœloplegmida an odd, very large main tube (the nasal style) arises from the anterior apex of each galea and bears on its base an odd frenulum. This nasal style and its frenulum is altogether wanting in the Cœlotholida, where two paired main tubes (the frontal tubes) arise from the lateral corners of the truncate anterior side of the galea, and are connected with the mouth of the rhinocanna by two paired convergent lateral frenula.

We distinguish in all Cœlographida two different forms of hollow branched tubes, which we will call "brushes" and "styles." The brushes are dichotomously branched from the base, not verticillate; their distal ramules remain separate in the Cœlotholida and compose the spiny surface, of the peculiar "fork-thicket" whilst in the Cœlographida they become connected by frequent anastomoses and form the outer "lattice-mantle." The styles however are much longer projecting over the surface of the thicket or the mantle, and are not dichotomously branched, but verticillate, or armed with cruciate or alternately cruciate pairs of branches; the larger branches of the styles may be again dichotomously branched like the brushes; whilst the free prominent parts of the styles are always verticillate or cruciate-pinnate. The brushes are identical with the hollow tubes of the Cœlodendrida, whilst the styles are peculiar forms of apophyses, wanting in the latter.

The minimum number of hollow tubes which arise from each valve is three, and these are probably homologous with the three primary tubes of the Cœlodendrida. Two of these are paired (right and left), whilst the third is odd and lies in the sagittal plane; they have the same position as in the tripodal Nassellaria, and may therefore bear the same names, the two paired anterior or pectoral tubes being divergent forwards, the odd or caudal tube being bisected backwards (so in the Cœlotholida, Pl. 121). The odd caudal tube (probably identical with the odd tube of the Cœlodendrida) is always a brush, dichotomously branched, and never prolonged into free style. The two paired frontal or pectoral tubes, however are usually prolonged into two long verticillate styles. The basal origin also of these three primary tubes is different. The two pectoral or anterior paired tubes always arise from the galea itself whilst the posterior odd or caudal tube usually arises behind the galea from the valve (Pl. 127, figs. 4-8, g 6).

Since these three primary tubes the odd caudal and the paired pectoral, are probably homologous in all Cœlographida and Cœlodendrida, they have a great morphological importance, similar to the three primary feet of the Nassellaria. All other tubes arising from the valves must be regarded as secondary apophyses, since they are not constant in all members of the two families, but present only in some of them. All the Cœlotholida observed (a small number of species only) possess no secondary tubes, but only the three primary; whilst all Cœloplegmida possess one or more secondary tubes, and one of these is constant, viz., the odd nasal style, directed towards the mouth, and arising as the foremost from the apex of the galea (Pl. 127, figs. 4-8, g 1).

The maximum number of tubes observed, which arise from each valve in the Cœloplegmida, is eleven; five of these are odd and placed in the sagittal plane of the body, viz.:—(A) the primary caudal tube (Pl. 127, figs. 4-8, g 6); (B) an odd procaudal tube, arising between the caudal and the sagittal tube; (C) the sagittal tube, placed either in the sagittal axis of the body or near it (often prolonged into a sagittal style, Pl. 128, fig. 1); (D) an odd postnasal tube, arising between the sagittal and the nasal tube; (E) the odd nasal tube, constant in all Cœloplegmida, and connected at its base by the odd frenulum with the rhinocanna (Pl. 127, figs. 4-8, g 1). All other tubes occurring in the Cœloplegmida are paired, and symmetrically arranged on both sides of the sagittal plane, at right and left; their maximum number is three pairs, viz.:—(F) the paired pectoral tubes (as the foremost), directed forwards; (G) the paired frontal or lateral tubes, placed either in the frontal axis of the valve, or in a neighbouring axis, directed towards the right and left pole (Pl. 127, figs. 4-8, g 4 and g 5); (H) the paired tergal tubes, directed backwards (constant in all Cœloplegmida). The origin of these tubes is rather variable, since they arise in nearly allied species, sometimes independently of one another, at other times united at the base. But a closer comparison of them in the different species will demonstrate their homology, caused by constant heredity.

The terminal ramules of the brushes, which form the subspherical "fork-thicket" in the Cœlotholida, the outer "lattice-mantle" in the Cœloplegmida, are constantly armed at the distal ends either with spathillæ or with anchor-pencils, bunches of those most elegant spinulate threads, which bear at the free end an anchor, or a whorl of two, three, or four recurved teeth (Pl. 122, fig. 8; Pl. 127, fig. 10; Pl. 128, figs. 1, 6). The pencils are usually dichotomously branched, their threads zig-zag or delicately serrate, often armed with very small recurved denticles, and the anchor teeth (commonly three or four) are usually smooth on the convex outer, serrate on the concave inner edge. The entire surface of the subspherical thicket in the Cœlotholida, and of the polyhedral lattice-mantle in the Cœloplegmida, is armed with thousands of those most elegant spathillæ, or anchor-pencils.

The "fork-thicket" of the Cœlotholida is identical with that of the Cœlodendrida, and is composed only of the innumerable dichotomous branches of the hollow tubes. It envelops the two central valves and the enclosed central capsule in the same way as in the Cœlodendrida. But the Cœlotholida differ from these latter in constantly possessing a rhinocanna and two frenulæ. The entire form of this thicket, which in the few species observed was never complete, but always more or less destroyed, is usually probably subspherical or polyhedral, sometimes cordate or kidney-shaped. Its surface is densely studded with thousands of spathillæ. Its diameter is about four to eight times as great as that of the enclosed bivalve shell.

The "lattice-mantle" of the Cœloplegmida, which replaces in this subfamily the fork-thicket of the Cœlotholida, is always produced by the anastomoses of the distal ramules of the brushes, and of those branches of the styles which do not proceed over the surface of the mantle. Its network is always very irregular, and composed of polygonal meshes of very different sizes. Usually it is quite simple, and may be compared with the cortical shell of the Disphærida. More rarely it is more or less spongy. Its surface is densely studded with thousands of spathillæ or anchor-pencils. The entire form of the lattice-mantle is always symmetrically polyhedral, since its dorsal and ventral halves are symmetrically developed on both sides of the equatorial plane, and therefore correspond perfectly to the enclosed smaller halves of the central bivalve shell. The two valves of the lattice-mantle (dorsal and ventral valves) are never really united and grown together, but are in loose contact in the equatorial plane; here the free edges of both valves catch into one another by means of free ramules (Pl. 128, figs. 1, 7). This loose connection is similar to what occurs in the Conchopsida (or in the Concharida with dentate edges), but never so regular. The special form of the polyhedral lattice-mantle depends on the number, arrangement, and development of the styles, which proceed over its surface; it preserves the polyhedral form of the calymma, on the surface of which it is deposed.

The characteristic styles of the Cœlographida (which are never found in the preceding Cœlodendrida) are longer hollow tubes, symmetrically disposed on both valves. They are prominent over the surface of the fork-thicket in the Cœlotholida, of the lattice-mantle in the Cœloplegmida. They bear in these latter a peculiar terminal coronet on their distal end, whilst in the former this end is armed with large pencils of spathillæ. The styles may be forked once or twice at their base, but in their greatest part they are verticillate, and not dichotomously branched like the brushes. The lateral branches of the styles are usually very numerous and regularly cruciate in alternating opposite pairs. In the odd nasal style, e.g., the first and third pairs of opposite lateral branches usually lie in the frontal plane, the second and fourth in the sagittal plane, perpendicular to the former, and so on. A similar regular disposition of the lateral branches is found also in other styles, but not in all. There are certain styles in which the lateral branches are not opposite in pairs, but alternate or verticillate, and others in which they represent unequal branches of forks, so that each single segment of the branched style represents the stouter branch of a fork, and the appertaining lateral branch the thinner branch of the fork. Further accurate examinations are required to recognise the different laws of the ramification of the styles in the different forms of Cœlographida. The lateral branches of the styles are usually again dichotomously branched inside the lattice-mantle, and their distal ends pass over into its network. But the verticillate or cruciate branches, which arise from the free part of the styles outside the lattice-mantle, are always armed with the same elegant pencils of spathillæ which cover the surface of the fork-thicket in the Cœlotholida, the surface of the lattice-mantle in the Cœloplegmida. These pencils also are often regularly opposite in pairs, and the pairs alternate in two planes perpendicular one to another (Pl. 128, figs. 1, 4).

The terminal coronets are peculiar ornaments which protect the distal ends of the styles in the Cœloplegmida, whilst in the Cœlotholida these are armed with the usual pencils of spathillæ (Pl. 122, fig. 8). Each coronet is usually produced by the double, triple, or quadruple furcation of the free distal end of the style; therefore composed of four, eight, or sixteen terminal branches, which, on account of their peculiar form and function, we may call "fingers." More rarely the ramification of the coronets is more or less irregular, and sometimes the number of the fingers exceeds twenty or even thirty.

In the majority of species eight fingers are regularly disposed (Pl. 127, figs. 1-3; Pl. 128, figs. 1-8). Often too sixteen occur, rarely four only. Sometimes the fingers are placed nearly in one plane and form a hand. The form of the fingers is very variable and most characteristic of the individual species. Very often they have the shape of a human finger, and are smooth, spinulate, or armed with recurved hooks. The distal end of each finger often again bears a small coronet or a spathilla (Pl. 128, figs. 5-9), and sometimes it is arrow-shaped (Pl. 126, fig. 2a). All these apophyses of the terminal coronets as well as the anchor-pencils of the mantle and the finest branches of the tubes, are hollow and filled up by jelly.

The different number and arrangement of the styles offers the best means for the distinction of genera in the Cœlographida. The minimum number is six (Cœlographis, Pl. 126, fig. 1), the maximum number sixteen (Cœlothamnus, Pl. 122, fig. 3, and Cœlagalma, Pl. 126, fig. 4). Since the arrangement of the styles in both valves is constantly symmetrical, the fundamental form of the whole body is in all Cœloplegmida "amphithect," as in the Ctenophora. The longitudinal or main axis of the body is vertical, with two distinct poles; the proboscis of the central capsule and the two rhinocannæ are directed upwards, towards the oral pole; the caudal tube of each valve is directed downwards, towards the aboral pole. The two other axes of the body are unequal, horizontal, and perpendicular one to the other; each has two equal poles. On the poles of the sagittal axis lie the galeæ of the dorsal and ventral valves; on the poles of the frontal axis lie the two secondary openings or parapylae of the central capsule. The frontal fissure or the large cleft between the dorsal and ventral valves of the skeleton lies in the vertical frontal plane of the body, which is perpendicular to the vertical sagittal plane; the equatorial plane, however, is horizontal.

The central capsule of the Cœlographida exhibits the same shape and position as in the preceding Cœlodendrida. It is subspherical, slightly depressed in the direction of the main axis, and lies enclosed between the two central valves of the lattice-shell. Its three constant openings lie in the frontal plane, and therefore in the frontal fissure between the two valves. The astropyle, or the main-opening of the capsule, lies on the oral pole of the main axis, and its radiate operculum (d) is directed upwards; the curved proboscis arising from it (o) is prominent between the mouths of the two opposed rhinocannæ. The two lateral parapylæ or accessory openings lie on both sides of the aboral pole, on the right and left (Pl. 127, figs. 4-6). The large spheroidal or somewhat lenticular nucleus (n) is usually about half as broad as the capsule, and contains numerous nucleoli. The protoplasm around the nucleus contains many vacuoles, and in the oral part of the capsule (between nucleus and operculum) often numerous groups of crystals (Pl. 127, figs. 4-6k, 7). The double membrane of the central capsule exhibits the same shape as in the other Phæodaria.

The calymma, or the extracapsular jelly-veil, is in the Cœlographida very voluminous, and includes the entire skeleton, the fork-thicket of the Cœlotholida, the lattice-mantle of the Cœloplegmida, and also the prominent large styles. Only the distal ends of the latter (with the terminal coronets), and the anchor pencils, covering the surface of the thicket and the mantle, seem to project over the surface of the calymma. The entire form of the latter is therefore a symmetrical polyhedron. The phæodium fills up a small part only of the calymma, and is usually enclosed in the two galeæ and their rhinocannæ (Pl. 127, figs. 5, 9), but often also a part of the phæodium is scattered around the oral half of the central capsule.

Synopsis of the Genera of Cœlographida.

Subfamily 1. Cœlotholida, Haeckel.

Definition.—Cœlographida with two paired lateral frenula on each galea, and with free terminal branches on the hollow radial tubes, without an external lattice-mantle. Eight to sixteen long styles are prominent over the surface of the fork-thicket, which is composed of the caudal brush and the dichotomous basal branches of the styles.

Genus 731. Cœlotholus,^[347] n. gen.

Definition.—Cœlographida with two paired lateral frenula on each galea, without external lattice-mantle, armed with eight styles (two pairs of styles on each valve).