GENERA AJilD GEOTJPS OF THE ECHINOIDEA. 269 



and large-headed tridactyle pedicellariae on the ambulacra ; scat- 

 tered upon the test irregularly are long-stemmed, large, slender, 

 open-headed tridactyle pedicellariae. 



Becent. Caribbean Sea, Barbados, 82-185 fathoms. 



Section JPrymnadetes. (Subanal fasciole absent ; peripetalous 

 fasciole present.) 

 Genus Aceste, Wyv. Thomson, 1877, Voyage of the ' Challenger' 

 Atlantic, vol. i. p. 376, figs. 95, 96. A. Agassiz, 1881, Beport 

 ' Challenger ' JEchini, p. 195, pis. xxxii. & xxxiii a. Loven, 

 1883, Pourtalesia, pp. 53, 88, pi. xx. 



Test small and moderate in size, long, low, narrow, and ovoid or 

 obcordate in marginal outline, broadest anteriorly, where there is 

 a large deep groove dorsally ; narrowest posteriorly, and more or 

 less vertically or obliquely truncated there ; test rising gradually 

 from the anterior part to the posterior, gibbous vertex ; tumid 

 and broadest near tbe dorsum, narrow actinally ; the broad 

 abactinal groove extending far back from the anterior notch. 



Apical system very excentric posteriorly, placed at the vertex, 

 small ; two basal plates, each with a large genital pore ; the 

 madreporite small, and either between the plates or in the right 

 anterior basal plate ; radial plates small. 



Anterior ambulacrum very broad, placed in the anterior groove, 

 commencing far back ; the plates very broad, low, numerous ; the 

 pores simple near the apex and double along the abactinal groove, 

 single actinally, rows distant. Antero-lateral ambulacra flush 

 and apetalous; long, narrow, with tall, narrow plates ; those of 

 the anterior zone are small and uniporous ; the plates of the 

 posterior zone biporous. These ambulacra pass along the outside 

 of the anterior groove to the anterior third of the test and then 

 over the flanks to the peristome, and they are directed almost 

 transversely abactinally. Postero-lateral ambulacra broader than 

 the antero-lateral; plates high and narrow abactinally, flush, 

 apetalous, and uniporous ; actinally the plates are large and 

 long. 



Interradia : the antero-lateral narrow, the postero-lateral 

 broader, and with the plates 2 and 3 of zone a of the right 

 area united actinally. 



Peristome quite anterior, vertical, at the anterior and actinal 

 end of the groove, elliptical or subpentagonal, with a plated 

 membrane, the largest plates towards the outer part ; mouth 



