224 PEOP. p. M. DITNCAN-'S EETISION OF THE 



Ambulacra diverse, flush, or nearly so, the anterior apetalous, 

 with distant pairs of small round pores ; paired ambulacra large, 

 semipetaloid, open distally; outer pores of pairs elongate or 

 comma-shaped, the inner round ; beyond tlie petaloid portions, 

 which are not very long, the pairs are continued as small round 

 perforations in the large ambulacral plates to the peristome, 

 where the plates become low and where fairly numerous 

 pores are in peripodia ; interporiferous areas with miliaries only, 

 abactinally, with primary tubercles and miliaries actinally even 

 over the postero-lateral ambulacra or not. 



Interradia large, with primary tubercles scattered abactinaJly, 

 and others, more or less numerous, on the plates remote from the 

 sutures, erenulate and perforate, more numerous and crowded 

 actinally. 



Peristome excentric in front, large, semilunar, with a large 

 projecting labrum ; membrane plated. An amphisternum sloping 

 on either side to the posterior ambulacra. Periproct supra- 

 marginal, in the truncation, circular in outline, witli numerous 

 concentric plates. Spines variable, may be stout and long ab- 

 actinally or small, always small actinally, and numerous and 

 serrated, some spoon-shaped or broad at the top ; within cellular. 

 Abactinal tentacles branchial, those of the buccal region as pedi- 

 cells with a globose top, and with long internal spicules. Fas- 

 cioles absent, or a doubtful partial marginal. 

 Fossil. Eocene (?) : Cuba. 

 Recent. Caribbean Sea. 



The species described by Dames from the Eocene of the 

 Yicentin is a Plesiolampas. See the similar ambulacra (p. 193). 

 M. Cotteau has described Palceopneustes Antillarvmi, 1875, 

 from a probably Eocene formation in Cuba. 



II. Division P ry mnadetes. 



The prymnadete Spatangoidea have not a true subanal fasciole 

 enclosing a plastron, nor are the plates of the posterior ambulacra 

 modified as in the Prymnodesmia ; yet a linear fasciole may pass 

 beneath the periproct from a lateral or marginal or peripetalous 

 fasciole in some genera: one or more of the latter fascioles 

 present. 



Genus Hemiaster. 



Subgenus Tripylus. 



