GENERA AJSTD GBOUPS OF THE ECHINOIDEA. 187 



Grenus Phtllobeisstjs, Cotteau, 1857-58, Ech. foss. de VYonne, 

 vol. ii. p. 81. De Loriol, 1861, Anim. invert, de Mont SaUve, 

 p. 165 ; 1873, EcJi. Selv., Terr. Gret. p. 233, pis. xviii., six. 

 Cotteau, Peron Sf Gautliier, 1879, Ech. Foss. de VAlgerie, 

 fasc. 5, p. 157. 



Syn. Anthohrissus, Poniel. 



Test of moderate size, oblong, subcircular and rounded rather 

 higli in front, subtruueated posteriorly, swollen above, and 

 almost flat actinally. Summit subcentral. 



Apical system compact, with four perforated basal plates and 

 five perforated radial plates. 



Ambulacra petaloid, witb narrow poriferous zones ; inner 

 pores round ; outer pores elongate ; zones more or less open. 



Peristome slightly excentric in front, flush, pentagonal or may 

 be oblique, with phyllodes and bourrelets. Periproct on the 

 posterior surface at the top of a groove, variable in height, with 

 keeled edges; it becomes narrower, and diminishes at the pos- 

 terior edge. Tubercles small, scrobiculate, homogeneous, large 

 around the peristome. 



Fossil. Lower Cretaceous : England, Europe, N. Africa. 

 Jurassic : Europe. 



Grenus Cltpetjs, Klein, 1734, JVat. Disp. Fchin. Agassiz Sf Desor, 

 1817, Cat. Bais., Ann. ' d. Sci. Nat. vol. vii. p. 156. Desor, 

 1858, Synopsis, p. 275. Wright, 1859, FaL iSoc. Monogr., 

 Brit. Foss. Ech. Ool. Form. p. 360. 



Test rather thick, large, circular or somewhat pentagonal in 

 wavy marginal contour, more or less truncated behind, low, dis- 

 coidal, or slightly tumid dorsally, nearly flat actinally. 



Apical system small, excentric posteriorly, or rarely central, 

 with four triangular perforated basal plates, and a large madre- 

 porite which occupies the centre of the system, separating the 

 postero-lateral basals and touching the posterior pair of radial 

 plates, which are separated by long, narrow, interradial plates. 



Ambulacra wide, petaloid, not closing abaetinally, narrow at the 

 ambitus and actinally. Poriferous zones widening rapidly dor- 

 sally, and becoming equal in width (or more) to the very equally 

 wide interporif erous areas, then diminishing in width and becoming 

 very narrow, until midway between the ambitus and the peristome, 

 where the pairs are arranged in very oblique triplets forming a 



