Central capsules cylindrical, filiform, much elongated, ten to one hundred times, sometimes two hundred to four hundred times as long as broad, snake-shaped or worm-shaped, curved and contorted in the most irregular manner, often spiral or twisted into a large nodule. Numerous oil-vesicles constantly present, forming one series of globules in the axis of every capsule; distance of the globules, one from another, and also from the capsule-membrane, about equal to their diameter. (This interesting and very curious form was very frequently observed living by me in the Canary Islands, in January 1867; the jelly-colonies were commonly spherical, and contained fifty to two hundred or more capsules of very different size and form.)

Dimensions.—Length of the central capsules 1 to 10, sometimes 20 to 40 mm.; average breadth 0.1 mm.

Habitat.—Canary Islands, Lanzerote, Haeckel, surface.

8. Collozoum vermiforme, n. sp. (Pl. 3, figs. 6, 7).

Central capsules cylindrical, much elongated, five to ten times (sometimes twenty to fifty times) as long as broad, snake-shaped or worm-shaped, very irregularly curved and contorted. Numerous oil-globules constantly present, forming in the axis of every capsule a double series of alternating rose-coloured globules. (This species is nearly allied to the preceding; but its capsules are thicker and shorter, and the oil-vesicles in them are arranged not in a single, but in a double row.)

Dimensions.—Length of the central capsules 0.6 to 1.2 mm., sometimes 3 to 6 mm.; breadth 0.12.

Habitat.—Tropical Atlantic, near the west coast of Africa, Station 349, Canary Islands, surface.

Subgenus 4. Collodiscus, Haeckel.

Definition.—Form of the central capsules discoidal or lenticular, with one shortened axis.

9. Collozoum coeruleum, Haeckel.

Central capsule lenticular or discoidal, flattened, blue coloured, with one single oil-globule in the centre. Protoplasm containing numerous crystals and dark blue pigment-granules. Membrane very thick, double-edged. (Whilst at Messina in 1859 I found this form not constantly discoidal, in 1867 in the Canary Islands I observed it constantly lenticular.)

Dimensions.—Breadth of the central capsules 0.1 to 0.15, height 0.04 to 0.08.

Habitat.—Mediterranean (Messina), Atlantic (Canary Islands), surface.

10. Collozoum discoideum, n. sp.

Central capsule discoidal, flattened, transparent, with a ring of twenty to twenty-five oil-globules in its circular periphery (on the inside of the thin membrane).

Dimensions.—Breadth of the central capsules 0.2, height 0.05.

Habitat.—South Pacific (Juan Fernandez), Station 300, surface.

Subgenus 5. Collodastrum, Haeckel.

Definition.—Form of the central capsules irregular and indefinite, variable, commonly polyhedral or polygonal, or amœboid, often with irregular, finger-like processes.

11. Collozoum pelagicum, Haeckel.

Central capsules small, quite irregularly formed, roundish-polyhedral or depressed-polygonal, transparent, without oil-globules. Often many extracapsular oil-vesicles in the common jelly-body between the central capsules. Membrane very thin and delicate.

Dimensions.—Diameter of the central capsules 0.02 to 0.08.

Habitat.—Mediterranean, Messina, Haeckel; Naples, Brandt; surface.

12. Collozoum stellatum, n. sp.

Central capsules star-shaped, irregularly radiating, with a great number (eight to twenty or more) of radial, short, conical, acute processes, very variable in size and number. Membrane thin. In every capsule several (four to eight) oil-globules.

Dimensions.—Diameter of the central capsules 0.12 to 0.2.

Habitat.—Central Pacific, Station 274, surface.

13. Collozoum amœboides, n. sp. (Pl. 3, figs. 4, 5).

Central capsules amœbiform, of moderate size, quite irregularly formed, with a variable number of finger-like, obtuse, irregular prolongations (commonly three to six), very variable in size and form. Membrane thin. In the centre of every capsule one single oil-globule.

Dimensions.—Diameter of the central capsules 0.04 to 0.08.

Habitat.—Indian Ocean, Ceylon, Haeckel; Madagascar, Rabbe; surface.

Suborder II. BELOIDEA, Haeckel.

Definition.—Spumellaria with an imperfect skeleton, composed of numerous solid needles or spicula, scattered irregularly in the calymma.

The suborder Beloidea comprises all those Spumellaria which possess an imperfect or rudimentary skeleton, composed of a variable number of isolated spicula scattered in the extracapsulum. The suborder contains only two different families, the solitary Thalassosphærida (or Beloidea monozoa) and the associated Sphærozoida (or Beloidea polyzoa). Both families are very nearly allied, and differ only in one single character: the solitary life of the former, the social union of the latter. It seems to be merely a consequence of this difference that the cleavage of the nucleus commonly takes place very late in the former, very early in the latter.

Commonly, therefore, the full-grown Thalassosphærida (until immediately before their propagation) exhibit one single nucleus in the centre of the capsule, whilst in the Sphærozoida the capsule is distended with numerous small nuclei. In these latter the centre of the capsule usually contains one large oil-globule, whilst in the former oil-globules are either wanting or scattered in large numbers in the endoplasm, or disposed in one layer on the inside of the capsule membrane.

In the solitary Thalassosphærida each capsule is enclosed in its own peculiar spherical calymma, whilst in the associated Sphærozoida all the capsules of the colony are united into one common, very voluminous, alveolated calymma.

Family III. Thalassosphærida, Haeckel, 1862, (Pl. 2).

Thalassosphærida, Monogr. d. Radiol., p. 255.

Definition.—Beloidea solitaria.

The family Thalassosphærida comprises all solitary Spumellaria with an imperfect skeleton, composed of numerous solid needles or spicula, scattered around the central capsule in the calymma. The structure of the unicellular soft body is quite the same as in the Thalassicollida; it differs from these only in the possession of the extracapsular skeleton. All needles of this skeleton are solid siliceous spicula, never hollow, as in the similar Cannorrhaphida among the Phæodaria. In the special structure and form of the skeleton the Thalassosphærida agree perfectly with the well-known, colony-building Sphærozoida; they differ from these only by their hermit-like life and by some peculiarities derived from this solitary development.

The oldest known form of this family is probably the first Radiolarian, observed in the living state, described in 1834 by Meyen as Physematium atlanticum (see p. 35). A second form was figured in my Monograph (1862) as Thalassosphæra bifurca (p. 260, Taf. xii. fig. 1). A third form was there described under the name Thalassosphæra morum; this remarkable form was first observed by Johannes Müller, and figured under the name Thalassicolla morum (1858, Abhandl., p. 28, Taf. vii. figs. 1, 2). The same form was afterwards observed living by myself in the Mediterranean, as well as in the Atlantic, and in great numbers by the late Sir Wyville Thomson in the Pacific. The latter gave a good figure of it with some valuable remarks in his excellent work, The Atlantic (1877, vol. i. p. 233, fig. 51). He called this peculiar Rhizopod Calcaromma calcarea, on account of the very peculiar calcareous bodies "looking in outline like the rowels of spurs," which are accumulated in great quantity around the central capsule, in the calymma. Further investigations have convinced me that these peculiar stellate bodies of carbonate of lime, for which we propose the name "Calcastrella," are not parts of the skeleton produced by the Radiolarian, but foreign bodies picked up by its extracapsular sarcode (in the same way as the Coccoliths are picked up by Thalassicolla sanguinolenta = Myxobrachia!). These Calcastrella occur also in the calymma of some Discoidea and other Radiolaria; they are either unicellular calcareous Algæ, or foreign bodies of other origin. The Collodarium, however, described as Thalassicolla morum and Calcaromma calcarea, seems to be a simple Actissa, which has picked up a number of Calcastrella.

The Challenger collection has yielded a number of other true Thalassosphærida, which partly agree with Thalassosphæra in the simple structure of the unicellular body (resembling Actissa), and partly differ from it in the development of alveoles, either within or without the central capsule (similar to Thalassolampe and Thalassicolla). The solid siliceous spicula, which occur in great numbers scattered in the calymma, agree perfectly in form with the spicula of the colony-building Sphærozoida. A characteristic difference between the social and the solitary Beloidea seems to be determined by the cleavage of the nucleus, which takes place in the latter very late, in the former very early. Therefore in the large central capsule of the mature solitary Thalassosphærida, we commonly find one large nucleus in the centre, and a number of oil-globules around it in the endosarc, or disposed in one layer on the inside of the capsule-membrane (Pl. 2, figs. 2, 5); whereas in the much smaller associated capsules of the Sphærozoida one large oil-globule is placed commonly in the centre, and a great number of small nuclei scattered in the endoplasm (compare above, p. 24).

Synopsis of the Genera of Thalassosphærida.

Genus 7. Thalassosphæra,^[14] Haeckel, 1862, Monogr. d. Radiol., p. 259.

Definition.—Thalassosphærida without alveoles, with simple, unbranched, needle-shaped spicula in the calymma.

The genus Thalassosphæra was founded by me in 1862 for those solitary Collodaria in which the simple central capsule is surrounded by scattered solid spicula. I described these two different species, the new Thalassosphæra bifurca and the Thalassosphæra morum, which J. Müller had formerly called Thalassicolla morum. This latter form is characterised by peculiar calcareous bodies "looking in outline like the rowels of spurs, scattered irregularly in the gelatinous envelope," and was therefore afterwards called "Calcaromma calcarea" by Sir Wyville Thomson.^[15] As already mentioned above, these calcareous rowels are foreign bodies, picked up by an Actissa (see p. 29). I here confine the genus Thalassosphæra to those solitary Beloidea in which the body exhibits no alveoles, and the siliceous solid spicula in the calymma are quite simple needles.

Thalassosphæra belonium, n. sp.

Spicula thin cylindrical rods, more or less curved, pointed at both ends, with smooth surface (similar to the needles of Rhaphidozoum italicum). Central capsule spherical, three times as large as the central nucleus, without larger oil-globules.

Dimensions.—Diameter of the central capsule 0.1 to 0.12, length of the spicula 0.04 to 0.08.

Habitat.—Central Pacific, Station 272, surface.

Thalassosphæra rhaphidium, n. sp.

Spicula thick cylindrical rods, more or less curved, pointed at both ends, covered with numerous strong conical thorns, perpendicular to the axis. Central capsule spherical, four times as broad as the central nucleus, with twenty to thirty large oil-globules on the inside of the membrane.

Dimensions.—Diameter of the central capsule 0.2, length of the spicula 0.12 to 0.16.

Habitat.—Tropical Atlantic, Station 347, surface.

Genus 8. Thalassoxanthium,^[16] Haeckel, 1881, Prodromus, p. 470.

Definition.—Thalassosphærida without alveoles, with numerous branched or compound spicula in the calymma.

The genus Thalassoxanthium differs from the foregoing Thalassosphæra, by the ramification of the spicula, and has therefore the same relation to it as Sphærozoum to Belonozoum. The soft unicellular body is as simple as in Actissa, and exhibits alveoles neither in the capsule nor in the calymma.

Subgenus 1. Thalassoxanthella, Haeckel.

Definition.—Spicula not geminate, but simply radiate, consisting of three, four, or more needles or shanks, radiating in different directions from one and the same point; shanks now simple or needle-like, now furcate or branched.

1. Thalassoxanthium triactinium, n. sp.

Spicula all (or nearly all) triradiate, composed of three (or sometimes in a few spicula four) needle-like shanks of equal length, diverging from one common point. Shanks straight or somewhat curved, smooth, pointed. Central capsule pellucid, twice as broad as its dark nucleus, without larger oil-globules. Jelly-envelope very thin, with numerous xanthellæ.

Dimensions.—Diameter of the central capsule 0.1, of its nucleus 0.05, length of the spicule-shanks 0.6 to 0.8.

Habitat.—Central Pacific, Station 266, surface.

2. Thalassoxanthium triradiatum, n. sp.

Spicula all (or nearly all) triradiate, composed of three (or sometimes in a few spicula four) needle-like shanks of different length, diverging from one common point. Shanks curved or bent, covered with small conical thorns. Central capsule dark, three times as large as the nucleus, with numerous large oil-globules. Jelly-envelope thick, without xanthellæ.

Dimensions.—Diameter of the capsule 0.2, of the nucleus 0.07, length of the spicule-shanks 0.1 to 0.15.

Habitat.—South Pacific, Station 302, surface.

3. Thalassoxanthium medusinum, n. sp. (Pl. 2, fig. 5).

Spicula all (or nearly all) quadriradiate, irregular, composed of four (or sometimes in a few spicula three) needle-like shanks (mostly of unequal length), diverging from one common point. Shanks curved, pointed, thorny, covered with small spinules. Central capsule dusky, twice to three times as large as its dark central nucleus. On the inside of the membrane numerous large oil-globules. Jelly-envelope thin, with numerous xanthellæ.

Dimensions.—Diameter of the central capsule 0.45 to 0.5, of its nucleus 0.18 to 0.2.

Habitat.—North Pacific, Station 244, surface.

4. Thalassoxanthium hexactinium, n. sp.

Spicula all (or nearly all) hexaradiate, composed of six (or sometimes in a few spicula three) needle-like shanks, diverging in two opposite hemispheres (three needles upwards, three needles downwards). Shanks somewhat curved, pointed, smooth. Central capsule yellowish-brown, dark, four times as broad as its dark central nucleus. Jelly-envelope thick (about twice as broad as the capsule), with very numerous xanthellæ.

Dimensions.—Diameter of the central capsule 0.3 to 0.4, of its nucleus 0.1 to 0.12.

Habitat.—South Atlantic, Station 325, surface.

5. Thalassoxanthium cervicorne, n. sp. (Pl. 2, figs. 3, 4).

Spicula all triradiate, trichotomously branched, with three equal shanks, which diverge from one common point, and are again provided each with three branches on the distal end. These nine branches are commonly once or twice forked (each fork rarely provided with three ramules). The ramules are thin, unequal, curved, or bent, and the ramification nearly resembles a stag's horn. Central capsule transparent, without oil-globules, two to three times as broad as the dark nucleus, which contains one single long central nucleolus. Calymma thin, scarcely as thick as the radius of the nucleus.

Dimensions.—Diameter of the central capsule 0.2 to 0.25, of the nucleus 0.08 to 0.1, length of the spicula 0.05 to 0.15.

Habitat.—Central Pacific, Stations 271, 274, surface.

Subgenus 2. Thalassoxanthomma, Haeckel.

Definition.—Spicula all or partly geminate, consisting of one middle or axial rod, from the two poles of which diverge two, three, or more shanks in different directions. Shanks or needle-rays sometimes simple, needle-like, sometimes bifurcated or branched.

6. Thalassoxanthium furcatum, n. sp.

Spicula all (or nearly all) geminate and simply forked, composed of a simple axial rod and two simple, needle-like shanks on each end of it. Shanks straight, pointed, smooth, somewhat shorter than the middle rod. Central capsule yellowish, dark, three times as broad as its central dark nucleus; besides this a single oil-globule, nearly of the same size.

Dimensions.—Diameter of the central capsule 0.1, of its nucleus 0.03; length of the axial rod of the spicula 0.04, of its shanks 0.03.

Habitat.—Cape Verde Islands.

7. Thalassoxanthium bifurcum, Haeckel.

Spicula all geminate and double forked, composed of a simple axial rod and two forked branches on each end; these branches are again forked, so that each spiculum exhibits eight thin distal ends. All branches are thin, slender and straight. Central capsule red, four times as broad as the central nucleus, containing between the red pigment-granules numerous, peculiar, violin-shaped bodies (fat-corpuscles?). Compare fig. 1, loc. cit.

Dimensions.—Diameter of the central capsule 0.08, of the nucleus 0.02, length of the spicula 0.05 to 0.08.

Habitat.—Mediterranean (Messina), surface, Haeckel.

8. Thalassoxanthium ovodimare, n. sp.

Spicula all geminate, composed of a simple, very short axial rod and three diverging shanks or branches on each end of it; the shanks are very thin, straight, or little curved, and eight to ten times as long as the axial rod. The spicula are quite smooth, as in the similar Sphærozoum ovodimare (in which, however, the axial rod is much longer). Central capsule transparent, without oil-globules, twice as broad as the nucleus.

Dimensions.—Diameter of the capsule 0.4, of the nucleus 0.2, length of the spicula 0.1 to 0.2.

Habitat.—Central Pacific, Station 273, surface.

9. Thalassoxanthium punctatum, n. sp.

Spicula all geminate-triradiate, composed of a simple middle rod and of three diverging shanks on each end of it; the shanks are thorny with small spinules and shorter than the axial rod, very similar to the common Sphærozoum punctatum. Central capsule dark, with numerous (twenty to thirty) oil-globules on the inside of the membrane, three times as broad as the nucleus.

Dimensions.—Diameter of the capsule 0.3, of the nucleus 0.1, length of the spicula 0.05 to 0.2.

Habitat.—Central Pacific, Station 274, surface.

10. Thalassoxanthium octoceras, n. sp. (Pl. 2, fig. 6).

Spicula all geminate-quadriradiate, composed of a simple short middle rod and of four diverging shanks on each end of it; the shanks are quite smooth, irregularly curved or bent, and four to eight times as long as the middle rod. Central capsule dark, filled with pigment-granules, without oil-globules, four times as large as the nucleus.

Dimensions.—Diameter of the capsule 0.5, of the nucleus 0.12, length of the spicula 0.2 to 0.4.

Habitat.—Indian Ocean, Madagascar, Rabbe.

Genus 9. Physematium,^[17] Meyen, 1834, Nova Acta Acad. Nat. Curios., vol. xvi., Suppl., p. 286 (p. 162).

Definition.—Thalassosphærida with large numerous alveoles within the central capsule (not in the calymma), and with numerous simple, needle-shaped spicula in the calymma.

The genus Physematium is, together with the colony-forming Sphærozoum, the first Radiolarian which was observed in the living state, described in 1834 by Meyen. It is most nearly allied to Thalassolampe, and has the same large roundish alveoles within the central capsule, which reaches therefore an extraordinary size, 5 to 10 mm. It differs from the latter by the possession of spicula in the calymma. The peculiar "centripetale Zell-gruppen" on the inside of the capsule-membrane are probably due to radial cleavages of the endoplasm; as also occurs in other Collodaria.

1. Physematium mülleri, Schneider.

Spherical body limpid, somewhat opalescent, sometimes a little yellowish or brownish, rather soft. Central capsule with a thin, but firm, transparent membrane, its diameter eight to ten times as large as that of the central spherical nucleus. Membrane of the nucleus thick, porous, on its inside with some nucleoli. In the protoplasmic network between the large intracapsular alveoles, numerous large, pale, yellowish, or orange oil-globules. On the inside of the membrane numerous conical bodies, centripetally directed with the apex towards the centre; every conical body ("kegelförmige centripetale Zellgruppe") composed of three to nine (commonly four or five) nucleated cells (mother-cells of the spores?); in the axis of the cone there is often a yellowish, orange, or brown oil-globule. Extracapsular jelly-envelope thin, with short pseudopodia. Xanthellæ scarce or wanting. Spicula scattered in the jelly numerous, small, simple needles, commonly C- or S-like curved, smooth.

Dimensions.—Diameter of the whole jelly-sphere 3 to 6 mm., of the central capsule 1 to 5 mm., of the nucleus 0.1 to 0.5, length of the spicula 0.05 to 0.1.

Habitat.—Mediterranean, Messina; Schneider, Haeckel; surface.

2. Physematium atlanticum, Meyen.

Spherical body opalescent, pearl-like, with a violet or purple lustre, very soft. Central capsule with a strong, semi-transparent membrane, its diameter six to eight times as large as that of the central spherical nucleus. Membrane of the nucleus very thick, porous, on its inside with many small nucleoli. In the protoplasmic network between the alveoles very numerous, small, purple oil-globules. On the inside of the membrane a continuous simple layer of small nuclei, enclosed in radially striped protoplasm (mother-cells of the spores?). No centripetal conical bodies. Extracapsular jelly-envelope very thin, with short pseudopodia. No xanthellæ. Spicule scattered in the jelly numerous, small needles, straight or slightly curved, thorny owing to numerous small vertical spinules. This species and Thalassolampe maxima (p. 17) possess the largest central capsule.

Dimensions.—Diameter of the whole jelly-sphere 8 to 12 mm., of the central capsule 5 to 10 mm., of the nucleus 1 to 2 mm., length of the spicula 0.1 to 0.3.

Habitat.—Eastern Atlantic, between Canary Islands and Cape Verde Islands, Meyen; Lanzerote, Haeckel.

Genus 10. Thalassoplancta,^[18] Haeckel, 1862, Monogr. d. Radiol., p. 261.

Definition.—Thalassosphærida with numerous large alveoles in the calymma (but not in the central capsule), and with numerous simple, needle-shaped spicula around the central capsule.

The genus Thalassoplancta was founded by me in 1862 for a Radiolarian with simple hollow needles in the calymma, which was afterwards recognised as a Phæodarium, belonging to Cannorrhaphis. We here retain this name for a true Thalassosphærid, very similar to the latter, but distinguished by the absence of the phæodium and the solid—not hollow—needle-shaped spicula, which are scattered in the alveolated calymma. Thalassoplancta can be regarded as the solitary form of the social Belonozoum.^[19]

1. Thalassoplancta longispicula, n. sp.

Spicula long and thin, cylindrical, smooth, more or less bent, pointed at both ends, similar to those of Thalassoplancta cavispicula. Central capsule thin-walled, without oil-globules, four times as broad as the nucleus, which encloses one single nucleolus.

Dimensions.—Diameter of the capsule 0.6, of the nucleus 0.15, of the calymma 4 mm.

Habitat.—North Atlantic, Færöe Channel (Gulf Stream), John Murray.

2. Thalassoplancta brevispicula, n. sp. (Pl. 2, fig. 2).

Spicula short and thick, thorny, irregularly curved, pointed at both ends, very numerous. In the observed specimen all spicula were aggregated in the outer part of the voluminous calymma, whilst the inner alveolated part was devoid of them. Central capsule thick walled, with a layer of large oil-globules on its inner surface, twice as broad as the large nucleus which contains numerous nucleoli.

Dimensions.—Diameter of the central capsule 0.5, of the nucleus 0.2, of the calymma 2.5.

Habitat.—South Atlantic, Station 334, surface.

Genus 11. Lampoxanthium,^[20] n. gen.

Definition.—Thalassosphærida with numerous large alveoles in the calymma (but not in the central capsule), and with numerous branched or compound spicula in the calymma.

The genus Lampoxanthium differs from the foregoing, Thalassoplancta, by the composite form of the spicula, which are not simple needles, but radiate or geminate, or branched in different forms; the former stands therefore in the same relation to the latter as the social Belonozoum to Sphærozoum. The spicula of some species of Lampoxanthium are identical with those of some species of Sphærozoum, so that the latter may be derived from the former by forming colonies. The large central capsule is enveloped by a very voluminous alveolated calymma, and includes a large central nucleus with numerous nucleoli.

Subgenus 1. Lampoxanthella, Haeckel.

Definition.—Spicula all (or nearly all) of one kind, radiate.

1. Lampoxanthium tetractinium, n. sp.

Spicula all (or nearly all) tetraradiate, with four thorny, straight, pointed shanks, radiating from one common point. (Intermingled with these are often some few, thorny, triradiate spicula.) On the inside of the capsule a layer of large oil-globules as in Thalassoplancta, Pl. 2, fig. 2.

Dimensions.—Diameter of the central capsule 0.2, of the nucleus 0.08, of the calymma 0.8.

Habitat.—South Pacific, Station 288, surface.

Subgenus 2. Lampoxanthomma, Haeckel.

Definition.—Spicula all (or nearly all) of one kind, geminate-radiate, with a simple middle rod and two to four diverging shanks on each end of it.

2. Lampoxanthium punctatum, n. sp.

Spicula all geminate-triradiate, thorny, of the same form as in the common Sphærozoum punctatum, of which this species is the large solitary representative. The spicula are aggregated in a very condensed layer on the surface of the large calymma.

Dimensions.—Diameter of the capsule 0.8, of the nucleus 0.6, of the calymma 2.0.

Habitat.—North Pacific, Station 248, surface.

3. Lampoxanthium octoceras, n. sp.

Spicula all geminate-quadriradiate, with a very short simple middle rod and four very long divergent shanks on both ends of it; the shanks are smooth, five to ten times as long as the middle rod, irregularly bent and curved. (Differs from the similar Thalassoxanthium octoceras, Pl. 2, fig. 6, by slender, more curved shanks, and by the voluminous calymma, there entirely wanting.)

Dimensions.—Diameter of the capsule 0.5, of the nucleus 0.2, of the calymma 3.0.

Habitat.—South Atlantic, Station 331, surface.

Subgenus 3. Lampoxanthura, Haeckel.

Definition.—Spicula of two or three different kinds, simple, radiate, and geminate-radiate mixed.

4. Lampoxanthium pandora, n. sp. (Pl. 2, fig. 1).

Spicula mixed, of three different kinds—simple, radiate and geminate-radiate; all three kinds partly smooth, partly thorny. The simple needles short, thin spindle-shaped, often curved. The radiate spicula commonly with three or four, rarely five or six, unequal rays, straight or curved. The radiate-geminate spicula commonly with three, rarely four, shanks on each end, often different on both ends of the middle rod. The size, number, and form of the irregular spicula are here quite as variable as in the social Rhaphidozoum pandora, of which it is the solitary representative. The wall of the large central capsule is very thick, with evident pore-canals, separated by a clear interval from the coagulated and vacuolated endoplasm, which contains no oil-globules. Nucleus with numerous nucleoli.

Dimensions.—Diameter of the central capsule 0.5 to 0.6, of the nucleus 0.1 to 0.2, of the calymma 2 to 4 mm.

Habitat.—North Pacific, Station 244, surface.

Family IV. Sphærozoida, Haeckel (Pl. 4).

Sphærozoida, Haeckel, 1862, Monogr. d. Radiol., p. 521.

Definition.—Beloidea socialia.

The family Sphærozoida comprises all associated or colony-forming Radiolaria, which are provided with an imperfect skeleton, composed of numerous solid needles or spicula, scattered around the central capsule in the calymma. The structure and form of this skeleton is quite the same as in the preceding solitary Thalassosphærida, but on the other hand, the structure and form of the colonies and of the included numerous central capsules is the same as in the skeletonless Collozoida.

The oldest well-known form of Sphærozoida is the common cosmopolitan Sphærozoum punctatum, probably first observed in 1834 by Meyen, and called Sphærozoum fuscum, afterwards more accurately described by Huxley in 1851.

Other forms were afterwards described by Müller and by myself in 1862.^[21] Further investigations have shown me that some species of this family are among the most common Radiolaria, and occur in astonishing numbers on the surface of all warmer seas. But the number of species is comparatively small, and their distinction is very difficult, as all the different forms are very variable and connected by intermediate forms—a truly "transformistic" group.

The only character sufficient for the constitution of genera in this transformistic group is found in the form and composition of the spicula; the very variable form of the jelly-calymma and the enclosed central capsule being without value for this purpose. But also the form of the spicula is very variable, and not always constant. In some species the particular form of the spicula is transmitted by constant heredity, whilst in others it is very inconstant, even in one and the same individual. (Compare the remarks on variability in the general introduction.)

As the number of various forms is rather great, it seems to be advisable to distinguish the three following genera.

Synopsis of the Genera of Sphærozoida.

Genus 12. Belonozoum,^[22] n. gen.

Definition.—Sphærozoida with simple needle-shaped spicula, which are neither radiate nor branched.

The genus Belonozoum comprises the Sphærozoida with simple needle-shaped spicula, and may be regarded as the colonial form of Thalassosphæra or Thalassoplancta, derived from these solitary Beloidea by multiplication of the capsules and union in a common calymma.

1. Belonozoum bacillosum, n. sp.