. The Danish Ingolf-Expedition. Scientific expeditions; Arctic Ocean. io2 ECHINOIDEA. II. area. The bathymetrical distribution is from 220 (or 170, eomp. below, //. Mentzi) to 1700 fathoms (^Talisman ). Besides the species H. expergitus four more recent species of the genus Hemiaster (excl. Abatus) have been described, viz. Hemiaster gibbosus A. Ag., zonatus A. Ag. both from the '.Challenger-, H. Mentzi A. Ag., from the «Blake», and II. florigerus Studer, from the Gazelle . (The Hemiaster apicatus Woods is referred by Woods himself to the subgenus Rhinobrissus and therefore, being no true He
. The Danish Ingolf-Expedition. Scientific expeditions; Arctic Ocean. io2 ECHINOIDEA. II. area. The bathymetrical distribution is from 220 (or 170, eomp. below, //. Mentzi) to 1700 fathoms (^Talisman ). Besides the species H. expergitus four more recent species of the genus Hemiaster (excl. Abatus) have been described, viz. Hemiaster gibbosus A. Ag., zonatus A. Ag. both from the '.Challenger-, H. Mentzi A. Ag., from the «Blake», and II. florigerus Studer, from the Gazelle . (The Hemiaster apicatus Woods is referred by Woods himself to the subgenus Rhinobrissus and therefore, being no true Hemiaster, 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. 1S4, PI. XX. 5 â 16, 22) Agassi z does not point out by which features this species is distinguished from II. 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, 20'n'" in length; I have thus been able to compare the species with equal-sized specimens of H. expergitus, and finally I have examined the Challenger -specimens in the British Museum. The comparison of //. gibbosus and expergitus gives the following results. The shape of the testis the same; to be sure I have seen no specimen of expergitus 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 ' is almost quite as in expergitus. (Comp. PI. II. Fig. 1). Evidently the form
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