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clxxxvi hypothetical genealogical tree, which I then published, has been still further carried out in Chapter VI. of the present Introduction (see §§ 153-200).

253. General Survey of the Growth of our Systematic Acquaintance with the Radiolaria from 1834 to 1885.

1834. (L. N. 1) describes 2 genera and species of :—Sphærozoum fuscum and Physematium atlanticum.

1838. (L. N. 2) founds the family Polycystina upon 3 fossil genera (with 6 species):—Lithocampe, Cornutella, Haliomma.

1847. (L. N. 4) publishes his preliminary communications regarding the fossil Polycystina of Barbados and distinguishes 282 species, distributed in 44 genera and 7 families. In the tabular view of the genera he distinguishes two orders:—I. —(1) Halicalyptrina, (2) Lithochytrina, (3) Eucyrtidina; and II. —(4) Spyridina, (5) Calodictya, (6) Haliommatina, (7) Lithocyclidina (compare L. N. 16, pp. 214-219).

1851. (L. N. 5) gives the first accurate account of living Radiolaria, and describes 2 species of the genus Thalassicolla (nucleata and punctata); under the latter are included 4 genera of :—Collozoum, Sphærozoum, Collosphæra, Siphonosphæra (compare L. N. 16, pp. 12-14).

1854. (L. N. 6) publishes in his Mikrogeologie, figures of seventy-two species of fossil Polycystina (without descriptions).

1855. (L. N. 8, p. 248) describes the first Acanthometra, and elucidates its affinity to Huxley's Thalassicolla and Ehrenberg's Polycystina.

1858. (L. N. 12) establishes the new group Radiolaria as a special order of the Rhizopoda, and includes in it the Thalassicolla, Polycystina, and Acanthometra as closely related families. He opposes these radiate Rhizopoda to the Polythalamia, and describes 50 species observed by him living in the Mediterranean, these he arranges in 20 genera, of which 10 are new. The figures are contained in eleven plates (see L. N. 16, pp. 22-24).

1858. (L. N. 14) describes the first  (Plagiacantha arachnoides) and two species of Acanthometra, which he had observed living in Norway (see L. N. 16, p. 18).

1860. (L. N. 4) gives a short diagnosis of 22 new genera of Polycystina, based on the investigation of numerous deep-sea species brought up by Brooke from the depths of the Pacific Ocean. The number of his genera is thus increased to 66 (compare L. N. 16, pp. 10, 11).

1862. (L. N. 16) embraces in his Monograph of the Radiolaria all the species hitherto known either by figures or descriptions, and arranges them in 15 families and 113 genera; of which latter 46 are new. The number of new species observed living amounts to 144. In a "survey of the Radiolarian fauna of Messina" (p. 565) he records 72 genera and 169 species. Most of these are figured in the accompanying atlas of thirty-five plates.