IHERINCKLLA 1393 



inward and forward, without sculpture ; epidermis dull olive, 

 cloth-like ; hinge teeth imperfectly developed, nodulous or 

 broken more or less into denticles, there being- an irregular 

 tooth in the left valve under the beak, sometimes partially 

 bifid, and two in the right valve, with the pit between them 

 under the beak ; anterior muscle scars deep, more less united ; 

 posterior scars shallow ; nacre soft, bluish-silvery, iridescent 

 behind. 



Animal unknown. 



Type, Plagiodon isocardioidcs Lea. 



In Iheringdla the hinge teeth are even more irregular than 

 in Monocondylcca. They are more or less tuberculate or often 

 studded with irregular pustules and are sometimes more or 

 less longitudinal. 



Kky to spkctivS of Iheringeij.a. 



vShell much intiated, rhomboid or subrhomboid. 



vSurface smooth. isocardioides. 



Surface more or less cancellated. semisiilcata. 

 Shell only moderately inflated. 



Outline roimded. rotundata. 



Rotund triangular. bal.'sani. 



Group of Iheringella isocardioides. 



Shell rhomboid or /jforarrf/a-shaped, with a high, distinct, 

 strongly curved posterior ridge ; beaks decidedly full and 

 turned forward. 



iHKRfNGKLLA IS0C-\J{DIO!DKS (I^ea). 



Shell smooth, subtriangular or subrhomboid, greatly inflated, 

 inequilateral, subsolid or rather thin ; beaks very full and high, 

 turned forward and inward ; posterior ridge well developed, 

 subangulate ; anterior and posterior ends almost squarely sub- 

 truncate ; hinge line arched ; base nearly straight ; epidermis 

 dull olive ; teeth imperfect, nodulous, short, the upper division 

 longer, double in each valve ; anterior scars deep and confluent ; 



