GENEBA AND GROUPS OP THE ECHINOIDEA. 207 



interradia enter the peristome with single plates, and that of the 

 posterior is a labrum, behind which is a many-plated merido- 

 sternum forming a long plastron. 



Peristome excentric in front, transversely oval ; phyllodes 

 moderately developed. Periproet inframarginal, posterior, oval. 



Ornamentation of scanty small primary tubercles and nume- 

 rous small granules ; spines short and small. 



JFossil. Upper Cretaceous : England, Europe, Africa. 



Subgenus Jeeokia, Seunes, 1888 (genus), JBull. Soc. Geol. de 

 France, ser. 8, vol. xvi. p. 809. 



Test large, subrostrate behind. Ambulacral plates broad and 

 large. Apical system may have an accessory plate and only three 

 genital pores. Some large tubercles near the ambitus. 



Fossil. Cretaceous : Europe. 



Grenus Holastee, Agassiz, 1840, Gatal. Sysf. p. 1 ; 1847, Ann. d. 



8ci. Nat. ser. 3, vol. viii. p. 26. Desor, 1858, Synopsis, p. 336. 



Fictet, 1872, Fal. Suisse, Ech. Gret. p. 292. Loven, 1874, 



Etudes, p. 49, pis, v. & xxv. 



Syn. Guettaria, Gauthier, 1887; Fntomaster, Gauthier, 1887. 



Test variable in size, thin, ovoid in marginal outline, flat acti- 

 nally, tumid and high, and may be keeled abactinally ; a very 

 broad and shallow groove anteriorly. 



Apical system elongate ; the madreporite in the right anterior 

 basal plate. 



Ambulacra apetalous, biporous, diverse; the aijterior ambu- 

 lacrum with pairs of small, oblique, circular or slightly elongate 

 pores in the groove ; the antero-lateral ambulacra the most di- 

 vergent, their pores oblique, diverse, circular and linear, rather 

 long ; the pairs of the anterior and posterior zones may differ in 

 size ; the postero-lateral similar to the antero-lateral abactinally, 

 like them also in having minute wide-apart pairs at the ambitus, 

 but differing in being long and broad on the sides of the actinal 

 plastron. 



Interradia with large plates ; the postero-lateral area of the right 

 side actinally has the second plates of both zones beyond the single 

 peristomial plate united, aud is thus unlike the corresponding 

 area of the left side ; the peristomial plate of the posterior inter- 

 radium is broad and larger than the others, it forms a labrum 

 and is succeeded by a long many-plated meridosternum, but the 



