212 PEOP. p. M. Duncan's eeyision op the 



moreover (as Loven has pointed out), without the peculiar ar- 

 rangement of the pores of the postero-lateral ambulacra in the sub- 

 anal region, which is seen invariably with a true subanal fasciole. 

 It may be that there are two groups of forms, one without and 

 the other with a subanal fasciole, and yet closely allied, as in the 

 instance of Micraster and Epiaster ; or the fasciole may be so 

 small in the area which it surrounds, that it does not interfere 

 with the ambulacra. The final solution of these questions 

 must be left to the distinguished author of the Eeport on the 

 ' Challenger ' Echini ; but for the present the latest authority, 

 Prof. Loven, must be consulted. 



Grenus TJEEOHi]srTrs, A. Agassiz, 1879, Proc. Amer. Acad. vol. xiv. 



p. 207 ; 1881, Report on the ' Ohallenger ' EcJiini, p. 146, 



pis. xxix., xxs., XXX. a ; 1883, Report on the ^BlaTce ' Echini, 



p. 52, pi. xxvi. Loven, 1883, Pourtalesia, p. 90, pi. xxi. 



Test moderate in size, ovoid, tumid, tapering posteriorly in 



marginal outline, varying in height, either low, tumid, and feebly 



arched dorsally, or conical and taller than broad ; convex acti- 



nally, with a slight keel over the region behind the peristome, 



truncated posteriorly, and with a hood overhanging the periproct ; 



surface smooth. 



Apical system nearly central, elongate, the lateral basal plates 

 separatedby the junction of the antero-lateral radial plates, with 

 or without complementary plates ; usually three genital pores ; 

 and the madreporite in the right anterior basal plate, but there 

 may be a fourth pore ; posterior basal plates united ; radial plates 

 irregular in shape. 



Ambulacra all flush, apetalous, uniporous ; the plates high, 

 and differing little from those of the interradia, except those of 

 the anterior, which are lower and more numerous ; pores small. 



Interradia with the postero-lateral areas broadest ; actinally the 

 single peristomial plates small and narrow, the labrum also 

 and not prominent ; the whole of the paired areas symmetrical j 

 the second plates of both zones of each lateral interradium 

 united so as to form a single plate beyond the peristomial 

 plate; the third plates separate. The sternum semimerido- 

 sternous (the plate 2 of zone h occupying the whole sternum, 

 and followed by a small plate 2 of zone a, and at its side a plate 

 3 of zone 6). 



Peristome subcentral in front, slightly sunken, subpentagonal ; 



