222 FOREIGN JURASSIC STOMECHINL 



Stomechinus apertus, Desor. Synopsis des Echinides Fossiles, p. 127. 



Test sub-conica], pentagonal ; ambulacra with two rows of tubercles, a little less in 

 size, but more numerous than in the inter-ambulacra, which have six rows of tubercles at 

 the circumference ; mouth opening very large. " This species was formerly confounded 

 with UcJdnus excavatus, Goldf., which has the ambulacral tubercles much smaller, and 

 set more close together than those of the inter-ambulacra^ whilst in Stomechinus apertus their 

 difference in size is scarcely perceptible." Desor. 



Formation. — Kellovien de maroiles pres Maiiiers, Courgains, Nantua, Rare. 



Collections. — M. Michelin, d'Orbigiiy, Paris Museum. 



Stomechinus Robin aldinus, Cotteau. Syn. Echinus Bobinaldinus, Cotteau. Etudes 



sur les Echinides Fossiles, pi. 22, figs. 1 — 6. 



Test sub-conoidal, inflated at the sides ; circumference sub-circular ; ambulacra with 

 four regular rows of tubercles, identical with those of the inter- ambulacra ; poriferous zones 

 wide, trigeminal ranks very oblique ; inter-ambulacra double the width of the ambulacra, 

 and covered throughout with equal-sized tubercles, regularly disposed in numerous series, 

 six tubercles on each plate ; apical disc composed of equal-sized genital plates ; vent large ; 

 mouth opening moderate in width, in the proportion of one to two and a half; peristome 

 decagonal, with wide, obtuse notches. 



Dimensions. — Height, one inch and a half ; transverse diameter, two inches and one 

 fifth. 



Formation. — " Cette espece caracterise les couches superieures de I'etage Corallien et 

 n'a jamais ete rencontree dans le Coral-rag inferieur de Chatel- 

 Censoir et de Druyes." Cotteau. 



Collection. — M. Robineau-Desvoidy. Very rare ; only three specimens known. 



