200 THE VOYAGE OF H.M.S. CHALLENG'EE. 



on the one hand but a step to species which have been associated with Prenaster, leading 

 to Pencosmus, and which in their turn lead most naturally to Meter opneustes, and of 

 such types as Brissomorpha of Laube, in which the peiipetalous fasciole has completely 

 disappeared ; while in another direction the structure of these species would also indicate 

 affinities to such genera as Faorina, which in their turn lead to such genera as Cyclaster, 

 to which many fossil species are frequently referred without reference to the presence or 

 absence of a peripetalous fasciole. 



We have not as yet sufficient data, for the study of the young Schizaster, to enter 

 into very detailed comparisons, but the following points are interesting as throwing 

 additional light on the affinities of the genera allied to the Schizasteridag : — 



The limits which have been assigned to the genera closely allied to Schizaster are 

 very unsatisfactory, and the generic characters by which different species are assigned to 

 these genera or sub-genera pass so gradually one into the other, not merely among the 

 recent species, but especially when we come to include the fossil species, that the task of 

 properly limiting them appears hopeless, although these characters are convenient as 

 subdivisions according to which we may associate groups of species. 



Take, for instance, species like Schizaster canaliferus, with a broad, deep sunken 

 anterior ambulacrum, a short posterior lateral pair of ambulacra, and a well-developed 

 lateral fasciole extending under the anal system, and they seem to form a well-marked 

 group when contrasted to species like Schizaster moseleyi, in which the test is compara- 

 tively flattened, the anterior ambulacrum broad but shallow, and where no lateral fasciole 

 exists, having the course of that of Schizaster canaliferus, or but slight traces of it, exist 

 as an indistinct branch of an anal fasciole ; while in other species Schizaster fragilis and 

 Schizaster philippii, having the same general facies as Schizaster moseleyi, we have not 

 thus far found the variation in the course and extent of this lateral fasciole, but it is quite 

 as well defined as in Schizaster canaliferus ; while again such a group as that to Avlii(;h 

 Schizaster ventricosus and Schizaster gibherulus belong has the more deeply sunken 

 ambulacra of Schizaster canaliferus, without a lateral fasciole but very distinct anal 

 fasciole, and yet has the low flattened test of Schizaster pnhilippii and Schizaster fragilis. 



The small specimens (from 12-19 mm.) of young Schizaster ventricosus, Schizaster 

 japonicus, and Schizaster moseleyi collected by the Challenger, show already the specific 

 characters sufficiently well developed to enable us readUy to assign them to their respective 

 species ; the difference in outline in the test is, however, quite marked, and the test of all 

 these species is much more globular than in the adult, and in one specimen of Schizaster 

 moseleyi the test was, as in young specimens of Brissop)sis, nearly globular, with a slightly 

 indented peripetalous fesciole, and the suckers of the odd anterior ambulacrum already 

 developed out of proportion to the rest of the test. The anal fasciole is quite well marked 

 in the smallest specimens of Schizaster ventricosus, but the latero-anal fasciole of Schizaster 

 japonicus is occasionally interrupted on the sides of the test in small specimens, evidently 



