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Show 278 MR. F. P. BEDFORD ON MALAYAN ECHINODERMS. [ Mar. 20, 3. ASTHENOSOMA HETERACTIS, sp. nov. (Plate XXI. fig. 2.) References. Grube, 45es Jahresb. d. Schles. Gesell. f. vat. Cult. 1863 (A. varium). H. Ludwig, Zeitschr. f. wiss. Zool. Bd. 34,1880, p. 70 (A. varium). A. Agassiz, ' Challenger ' Exports, vol. iii. Echinoidea, 1880, p. 82 (A. grubei). P. & F. Sarasin, Ergeb. naturw. Forsch. Ceylon, Bd. i. Heft 3, 1888 (A. urens). S. Loven, Bih. till K. Sv. Vet.-.Ak. Handl. Bd. 18, 1892 (A. varium). F. J. Bell, Ann. & Mag. IS at. Hist. (6) vol. iv. 1889, pp. 436-438. P. de Loriol, Eev. Suisse de Zool. t, i. & iii. 1893 & 1896 (A. varium). S. Yoshiwara, Ann. Zool. Jap. vol. i. part 1, 1897 (A. ijimai). R. Koehler, Zool. Anz. xx. 1897, p. 307. Locality Sf Habitat. This species occurs in some numbers in about 5 fathoms of water on a muddy bottom off the west of Pulo Brani, Singapore ; a single specimen was dredged by Dr. Hanitsch in the N e w Harbour, Singapore; it lives in company with a species of Haplodattyla, specimens being frequently obtained together in the dredge. This form is very closely allied to the other three shallow-water species of Asthenosoma; its adult characters appear to be very constant, and although its differences from these species are very slight, it seems advisable to regard it as a distinct species. The nearest ally is perhaps Asthenosoma urens, collected by the Drs. Sarasin in the north of Ceylon, which it resembles in the possession of thorn-bearing spines in the neighbourhood of the ambitus, as well as poison-organs arranged along each side of the interambulacral space, and in the former respect it differs at once from A. varium and A. grubei. It is distinguished from A. urens by the very marked distinction in appearance between the ambu-lacral and interambulacral abactinal spines ; the latter possess constricted connective-tissue sheaths as in all the abactinal spines of A. urens, which they also resemble in the possession of well developed poison-sacs, there is. however, very little pigment developed in their sheaths ; the ambulacral spines are of equal length to the interambulacral, but have a very thin sheath which is unconstricted, and they are marked by very distinct and regular bands of purple pigment arranged transversely at intervals along the sheath ; poison-sacs are also developed on these spines, but their tips are much more fragile than those of the other spines and in process of capture they are nearly always broken. The calycinal system resembles in the adult that of A. urens and A. grubei, and differs from A. varium in the separation of the genital pores from the genital plates, the pore being situated in a V-shaped incision on the outer margin of the plate. The madreporite differs from that of A. grubei in being quite flush with the rest of the calycinal system. The peristomal plates, of which there are ten rows continuous with the ambulacral coronal plates (the interradial plates being |
