IO2 



ECHINOIDEA. II. 



area. The bathymetrical distribution is from 220 (or 170, comp. below, H. Mcntzi) to 1700 fathoms 

 (Talisman). 



Besides the species H.expcrgitus four more recent species of the genus Plcmiastcr (excl. Abatus) 

 have been described, viz. Hcmiastcr gibbostis A. Ag., zonatus A. Ag. both from the Challengers, 

 H. Mentzi A. Ag., from the Blake, and //. florigerus Studer, from the Gazelle. (The Hcmiaster 

 apicatus Woods is referred by Woods himself to the subgenus Rhinobrissus and therefore, being no 

 true H&miaster, does not concern us here). As for the first and third of these species it seems rather 

 probable that they will prove to be synonyms only of H. expergitus. 



In his description of Hemiaster gibbosus (Chall.-Ech. p. 184, PI. XX. 5 16, 22) Agassiz does 

 not point out by which features this species is distinguished from H. expergitus, and a careful analysis 

 of his description and figures does not reveal any good distinguishing characters either. De Meijere 

 (Siboga-Ech. p. 182) has had some specimens of H. gibbosus, but he only remarks that he finds them 

 answering well to the description given by Agassiz. Through the kindness of Professor M. Weber 

 I have received one of these specimens, 2O mni in length; I have thus been able to compare the species 

 with equal-sized specimens of H. expergitus, and finally I have examined the Challengers-specimens 

 in the British Museum. The comparison of H. gibbosus and expergitus gives the following results. 



The shape of the test is the same; to be sure I have seen no specimen of cxpcrgittis of the form 

 shown in Fig. 6. PI. XX of the Challenger-Echini, all the specimens being wider in front than behind, 

 or (the small ones) almost elliptic. But Agassiz himself states that the outline is variable, and the outline 



of the specimen figured in PL XX. 5 T is almost quite as in expergitus. 

 (Comp. PL II. Fig. i). Evidently the form of the test thus does not give 

 any distinguishing character. Agassiz points out that the plates of 

 the lateral posterior interambnlacra are comparatively bare -- but in 

 expergitus they may be quite as bare, and I am unable to find any 

 difference herein between the specimen of gibbosus before me and 

 equal-sized expergitus. The biyium is separated from the trivium by 

 two large intercalated interambulacral plates*. I suppose, that by these 

 are meant the two large plates within the fascicle between the anterior 

 and posterior petal seen in the Fig. 9. PL XX. The figure, however, must 

 certainly be wrong. It would be a quite exceptional thing to find in 

 this place two large, paired plates; I find these interambulacra in the 



specimen before me of the usual structure (Fig. 19), the fasciole passes over the third and fourth plate, 

 quite as in expergitus of the same size. It could not be made out with certainty, how this is in the 

 Challenger-specimens, but I do not donbt in the slightest that they will show the usual structure. 

 (In the largest specimen of expergitus the fasciole traverses the 5th 7th plate in these interambu- 

 lacra). The intermiliary granulation*, which Professor Agassiz figures (PL XX. Fig. 13), I am unable 

 to find either in the specimen of gibbosiis or in expergitus of corresponding size. In the largest speci- 

 men of expergitus it is well developed, though not so close as in the figure quoted. 



Fig. 19. Abactinal part of the left 

 posterior Interambulacrum (4), of 

 Hemiaster gibbosus; comp. with 

 PI. XX. Fig. 9 of the Challenger- 

 Echinoidea. 



1 In the explanation of Plates (p. 292) it is stated that Fig. 5 and 6 represent the same specimen which is evidently 

 impossible and in contradiction to the text (p. 184). 



