GEIiTERA AKD QEOIIPS OF THE ECHIFOIDEA. 221 



f erences in the pairs of pores of the odd ambulacrum — the essen- 

 tial distinction — are sufficient to separate the genera. De Loriol 

 has expressed liis doubts, but is content to permit the distinction 

 to persist at present. It is not possible, however, to admit 

 Miotoxaster, Pomel, although De Loriol names species with the 

 title in his ' Faune Cret. du Portug.' 



The position of the next genus is doubtful, and it would at 

 first sight not be considered a Spatangoid; but Humbert's 

 drawing shows some very definite characters. 



G-enus Heteroi/AMPAS, Gotteau, 1862, Bev. et Mag. de Zool. 

 ser. 2, vol. xiv. p. 198, pi. ix. ; Cotteau, Feron Sf Gautliier, 

 1881, Ech.foss. de V Alger, fasc. 8, p. 151, pi. xv. 



Test rather large, cordiform in marginal outline, truncated 

 and narrow behind, tumid dorsally, longer than broad, highest 

 posteriorly, depressed, flat actinally. 



Apical system subcentral, large, with four largely perforated 

 basal plates, the madreporite separating the posterior basal plates, 

 and the autero-laterai radial plates intercalated, between the basal 

 plates ; the posterior radials in contact and separating the pos- 

 terior basals. 



Ambulacra narrow, subpetaloid, slightly open, in grooves, sub- 

 equal, similar ; poriferous zones abactinally, with large elongate 

 outer and smaller comma-shaped inner pores, placed transversely ; 

 beyond the petaloid parts the pairs are small and close to the 

 peristome, one. pore is much smaller than the other of a pair. 



Peristome excentric in front, subpentagonal, longest trans- 

 versely, widely open, without a floscelle ; with a posterior labrum. 

 Periproct oval, supramarginal. Tuberculation scanty. 



Fossil. Cretaceous : N. Africa. 



The genus is evidently closely allied both to Cassidulids and 

 Spatangoids, and should be placed near Echinospatagus. 



G-enus Meg-alastee, Duncan, 1877, Quart. Journ, Geol. Soc. 

 xxxiii. p. 61. 



Test large, elliptical in outline, with a deep anterior groove 

 and small posterior truncation, depressed tumid abactinally, flat 

 actinally. 



Apical system excentric in front, small, with four genital pores. 



Ambulacra diverse, the anterior in the broad deep groove 



