GEJVTEBA AND GROUPS OF THE ECHINOIDEA. 169 



Genus Echikojsieus, Yan Phelsum, 1774, Brief aan Cornelius 

 Nozeman. Leske, apiid Klein, 1778, p. 173. Besor, 1858, 

 Synopsis, p. 197. Loven, 1872, Etudes, pis. ix. and xv. 

 A. Agassiz, 1872-74, Revision, p. 332. Duncan, 1884, Geol. 

 Mag. p. 17. 



Test small, thin, elongate-ovoid in marginal outline, tumid 

 dorsally, flat actinally, depressed. 



Apical system central, small, compact; four basal plates per- 

 forated by ducts, tlie posterior pair united, sutures fused, fifth 

 basal absent ; the madreporite in the right anterior basal. Eadial 

 pores very small. 



-Ambulacra similar, flush, apetaloid, narrov^^, broadest above the 

 ambitus ; poriferous zones narrow, straight, sunken or not ; pairs 

 of pores numerous, in straight series, some are in low primaries 

 and others are in larger primaries associated with a small demi- 

 plate also carrying a pair. Tubercles of the interporiferous 

 areas crowded, sunken or not, small, simple, and without ma- 

 melons. 



Interradia with crowded tubercles resembling those of the 

 ambulacra ; but many small, glassy, spineless tubercles of epi- 

 stroma occur. 



Actinally the ambulacra are unequally broad, in consequence 

 of the obliquity of- the triangular, rounded-angled, large, central 

 peristome. This is longest between the interradia 2 and 4 and 

 the edge of ambulacrum v. At the peristomial margin the 

 interradia 2 and 4 have two plates, but all the others only have 

 one. The actinal membrane is covered with pentagonal plates, 

 ■whicb become more numerous towards the centre of the area and 

 the small mouth. 



Periproct inframarginal, large, long, oval, separated from 

 the peristome by a single interradial peristomial plate and the 

 succeeding pair of plates. The membrane without tentacles. 

 Periproctal plates large near the edge anteriorly. Spines short. 

 Ambulacral tentacles homoiopodous, disciferous. 



Fossil. Miocene : I^. America. Late Tertiary : Gruadeloupe, 

 Cuba. 



Recent. Caribbean Sea, Florida, Australia, Kingsraill Islands, 

 Zanzibar. 



