300 



Cypricardia ? RiGiDA (n. sp.) 



Sliell elongate quadrangular, a little widest at tlie posterior end. 

 Dorsal line straight, bounded hj a rather broad escutcheon, which is 

 more than half as long as the entire length of the shell. Anterior 

 end truncate, prolonged near the basal margin ; posterior extremity 

 obliquely truncate ; basal line straight, slightly emarginate, a little 

 anterior to the middle, by a shallow sinus which crosses the shell 

 from beak to base. Lunule large, deeply marked ; beaks small, flat- 

 tened on the umbones, and enrolled, situated anteriorly; umbonal 

 ridge very prominent and angular, extending from the beak to the 

 postero-basal angle. A second but less prominent ridge passes about 

 midway between the first and the dorsal line, the posterior margin 

 being very oblique between the end of this ridge and the dorsal line. 



Surface marked by sharp, closely-arranged lines, parallel to the 

 margin of the shell, which are bent at right angles as they cross the 

 umbonal ridge, and less abruptly at the minor ridge. Interior of the 

 shell (as shown on casts), with a sharp, muscular ridge, passing from 

 the anterior side of the beaks, with a forward curvature, about two- 

 thirds the distance across the shell. 



This shell is placed provisionally under the genus Cypricardia, 

 being closely related externally to that genus, from which it differs, 

 however, in the presence of an anterior muscular ridge, and therefore 

 cannot properly be considered as belonging to that genus. 



This character has been made a feature both in Nuculites of Conrad, 

 and Cleidopliorus of Hall ; but our shell differs from the first not only 

 in the absence of the hinge teeth, but also in the external characters. 

 From the latter genus it differs very much in the external form, and 

 in the presence of a distinct escutcheon and lunule, and most proba- 

 bly a partially external ligament. 



Genus Cypricardella, Hall. 

 Cypricardella quadrata (n. sp.) 



Shell small, general form sub-quadrangular, height equal to three- 

 fourths the length. Valves depressed convex, most ventricose a little 

 posterior to the beaks along the umbonal ridge. Hinge line slightly 

 arcuate, gradually sloping to the posterior truncation. Anterior end 

 oblique, longest near the antero-basal angle ; posterior end narrow, 

 squarely truncate ; basal line regularly rounded from the anterior to 

 the posterior truncation. Beaks minute, flattened on the umbones, 

 slightly incurved ; umbonal ridge angular, gently arcuate. Escutcheon 

 narrow, elongate, extending to near the extremity of the hinge line. 



Surface beautifully marked by fine, equal, concentric lines, which 

 are abruptly bent upwards as they cross the umbonal ridge. 



