﻿Neiv Genus and Siyecies of Cystideans. 291 



number. The anal region of Astrocystitcs, too, is lateral 

 and well defined, but no indications of any such region 

 have yet been observed in Aster ohlast its. The sumnut, 

 also, is very differently constructed in these two genera. 

 In AsteroUastus there is a central oral aperture, imme- 

 diately surrounded by five apical plates, and the 

 ambulacral areas, which are comparatively broad and 

 short, do not reach to the centre. No traces of the oral 

 aperture are visible anywhere on the summit of Astro- 

 ci/stites, the mouth in that genus being apparently 

 subtegminal, and the ambulacral areas, which are long and 

 narrow, extend to the centre, where their covering plates 

 interlock. 



The ambulacral areas of Astrocystitcs are somewhat like 

 those of Blastoidocrinus, but, in the latter genus (which is 

 still known only from the few fragments collected by E. 

 Billings from the Chazy limestone of the Island of 

 Montreal and its immediate vicinity, and from the 

 imperfect specimens from the •' Orthoceratitenkalk" of 

 Pulkowa, Kussia, described and figured by Friedrich 

 Schmidt) the spaces between them are completely filled 

 with the large deltoids, which, according to E. Billings, 

 " extend the whole length of the pseudambulacra." 



There are, also, apparently, some points of resemblance 

 between Astrocystites and CystoUastits, Volborth, but in 

 Zittel's description of the latter genus, which is the only 

 one that the writer has access to, there are said to be two 

 pectinated rhombs in the calyx, whereas no traces of such 

 structures have been observed in the dorsal cup of 

 Astrocystites. 



In 1874^ Schmidt expressed the opinion that Blastoi- 

 docrinus, Aster ohktstus, Mesites and Cystohlastus are all 

 cystidea which may be regarded as intermediate in their 

 characters between that class and the blastoids, and it 



1 "Memoires cle rAcadeinie Iiiiperiale des Sciences de St.-Petersbourg, Vlle 

 Serie, tome XXI., p. 25." 



