EEPOET ON THE ECHIKOIDEA. 107 



^'Linopneustes {Paleopneustes). 

 Paleopmustes, A. Agassiz, 1873, BuU. Mus. Comp. Zool., vol. iii. No. 8, p. 188. 



Since the preliminary examination of the specimens associated as Paleopneustes 

 murrayi, A. Agassiz/ I have referred to the same species a couple of smaller specimens 

 which throw considerable light on the specific characters of this species, and show that 

 both the peripetalous fasciole and the subanal exist in the smallest specimen examined 

 (PI. XXXV.^ fig. 9), so that it seems best for the present at least to place this species 

 in a sub-genus of Paleopnieustes {Linopneustes) difi"ering from Paleopneustes in having 

 both a peripetalous and a subanal fasciole, until we know something more of the changes 

 due to growth in Paleojyneustes proper. I am the more inclined to do this as the 

 typical Paleopneustes, forming as it does a link between the Ananch}i;id8e and Spa- 

 tangidse, appears fossU in the Tertiaries, Dames ^ having described a species of 

 Paleopneustes, which differs from the recent West Indian species in being more elongated 

 and having a flattened test and more petaloid ambulacra, resembling, in fact, more in its 

 outline the smaller specimens of Linoi^neustes murrayi, in which the test is comparatively 

 flatter than in the older stages, agreeing also with those younger stages in having fewer 

 and proportionally larger tubercles on the abactinal side of the test. The sub-genera 

 Linopneustes and Paleopneustes stand related to each other much as Pericosmus and 

 Macrop>neustes do as far as relates to the existence of a peripetalous fasciole. 



The relations between PaIeop)neustes, Linopneustes, Platyhrissus and Eupatagus are 

 extremely instructive ; as I stated in the description of small specimens of Linopneustes 

 murrayi, these resemble Eupatagus in having a peripetalous and a subanal fasciole, they 

 agree, however, with Paleopneustes in not having petaloid ambulacra. The flattened 

 tests of Platyhrissus and of Eiqoatagus connect them with the younger stages of 

 Linopneustes, and the facies of tuberculation of Linopneustes agrees well with that of 

 Platyhrissus, while Platyhrissus and the typical Paleopneustes agree in not having 

 fascioles, while the semipetaloid anterior lateral ambulacrum of Platyhrissus forms the 

 passage between such petaloid ambulacra as we find in Paleopneustes, Asterostoma, and 

 Oviclypeus, and the petaloid ambulacra of Eupatagus, Spatangus, Maretia, Nacop)atagu$, 

 and the like, the petals of which are all more or less open at the extremity and some- 

 times even show a slight tendency to divergence. 



It seems evident from the descriptions of Cotteau and D'Orbigny that there are two 

 distinct t}7)es in Asterostoma, one of which may prove identical with the typical 

 Paleop)neustes,^ while the other type is represented l)y what Dames has called 

 Oviclypeus,^ which has the peculiar ambulacral furrows on the actinal surface mentioned 

 by Cotteau in his original description of the genus Asterostoma. 



» A. Aga.ssiz, 1879, Proc. Am. Acad., vol. xiv. p. 210. 



2 Dames, 1877, Palseontog., vol. xxv. pi. viii. fig. 1. 



3 A. Agassiz, 1874, " Hassler" Zool., Results, lU. Cat. Mus. Comp. Zool., No. 8. 

 * Dames, 1877, Pala'ontog., vol. .\xv. pi. x. fig. 1. 



