BIVALVIA. 149 



Spec. Char. Testa tenid, orbiculari vel subpentangulari, vix cequilaterali, tumidd, sub- 

 obliqud; striis confertis, articulatis ; umbonibus prominulis, approximatis ; margine integro. 



Shell thin, orbicular, or somewhat of a pentangular outline, scarcely equilateral, 

 tumid, and rather oblique ; ornamented with numerous close-set articulated striae ; 

 beaks slightly prominent and close ; margin smooth. 



Diameter, l|-th of an inch. 



Locality. Cor. Crag, Ramsholt, and Sutton. 



Red Crag, Sutton. Recent, Corsica and Sicily. 



About a dozen specimens of this species in perfect condition have been obtained 

 by myself from the Coralline Crag at Ramsholt : a few with the valves united, and 

 one only from the Red Crag. 



Not having been able to obtain a specimen of the recent shell for comparison, its 

 identification is dependent upon the figures and descriptions above referred to, but 

 its outward form and ornamented exterior are so peculiar, that it is assigned to the 

 Mediterranean species without much hesitation. 



The hinge of the right valve is furnished with two primary diverging teeth, the 

 posterior one being bifid, while the left valve has three teeth ; the centre one of which 

 is large and double, or so deeply cleft, as to give that valve the appearance of having 

 four ; there are no distinct lateral teeth, though on the anterior side the lateral edges 

 interlock ; it has but an elongated fulcrum for the external ligament ; there are no 

 lunule : the two large impressions by the adductors, the anterior one being the smaller 

 and more narrow ; the impression by the mantle is large, deep, and rounded, ascending 

 beyond the middle of the shell, and extending over to the anterior side. In outline 

 it much resembles L. undata, and also in its very visible but somewhat irregular lines 

 of increase, but it differs in the possession of numerous radiating striae. The length 

 generally exceeds the height by about an eighth, but in some specimens there is no 

 difference. 



Hippagus.* Isaac Lea, 1833. 

 Verticobdia. S. Wood, MSS., 1842. 



Generic Character. " Shell cordate, inflated, without teeth ; beaks large, recurved, 

 margin slightly overwrapping beneath the beak : anterior cicatrix long, posterior 

 cicatrix round." 



The above is given by Lea in his ' Contributions to Geology/ as the diagnosis of a 

 genus proposed to be established upon a small fossil shell found in the United States, 

 in a Formation of the Older Tertiary Period, and it has been adopted by Philippi, who 

 has included in it a fossil from the Valley of the River Lamati, in Calabria, and as this 

 appears to be identical with our Crag Species, I have followed the latter Author in the 

 generic assignment. 



* Etym. Hippagus, a horse-ferry boat. 



