278 MB. k\ P. BEDFOBD ON MALAYAN ECHIN0EEBM8. [ Mar. 20, 



3. Asthenosoma heteeactis, 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 ' Re- 

 ports, vol. iii. Echinoidea, 1880, p. 82 (A. grubei). P. & 

 F. Sarasin, Ergeb. naturw. Forsch. Ceylon, Bd. i. Heft 3, 

 1888 (A. urens). S. Love'n, Bill, till K. Sv. Vet.-Ak. 

 Handl. Bd. 18, 1892 (A. varium). F. J. Bell, Ann. & 

 Mag. Nat. Hist. (6) vol. iv. 1889, pp. 436-438. P. de 

 Loriol, Rev. Suisse de Zool. t, i. & iii. 1893 & 1896 

 (A. varium). S. Toshiwara, Ann. Zool. Jap. vol. i. part 1, 

 1897 {A. ijimai). K. 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 iu the New Harbour, Singapore ; it lives in 

 company with a species of Haplodactyla, 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 de- 

 veloped 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 sjstem 

 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 



