598 CRETACEOUS PALEONTOLOGY. 



Supet-family ISOCARDIACEA. 



Family ISOOARDIIDAE. 



Genus Isocardia Lamark. 



Isocardia cliffwoodensis Weller. 



Plate LXVI., Figs. 10-12. 



1905. Isocardia cliffwoodensis Weller, Joui'. Geol., vol. 13, p. 



326, figs. 1-3. 

 1905. Isocardia cliffuitpodensis Weller, Ann. Rep. State Geol. N. 



J., for 1904, p. 135, pi. IS, figs. 1-3. 

 Descriptiom. — Shell subovate in outline, the dimensions of two 

 type specimens being: length, 18.5 mm. and 15.5 mm.; height, 

 14.5 mm. and 14 mm. ; convexity of one valve, 6.5 mm. and 6.5 

 mm. Anterior margin rounding regularly from beneath the beak 

 into the ventral margin or sometimes a little more sharply 

 rounded in the middle ; ventral margin broadly rounded ; posterior 

 margin rather sharply rounded below, sloping forward above to 

 the posterior extremity of the hinge-line with a gently convex 

 curvature. Valves ventricose on the umbo, the most prominent 

 portion situated anterior to the middle of the shell, the beaks 

 small, situated anteriorly, strongly incurved and directed for- 

 ward; the antero-umbonal slope abrupt, the posterior slope con- 

 vex, becoming more abrupt as it approaches the posterior margin. 

 Surface of the shell smooth. 



Remarks. — This species has been observed in the New Jersey 

 collections only in the form of internal casts. " Examples of the 

 same species, however, are in the collection of the National 

 Museum at Washington, from Corsicana, Texas, with the shell 

 preserved. The shell substance of these specimens is very thin 

 and the surface is marked only by fine concentric lines of growth. 

 The species exhibits some individual variation, especially in the 

 length of the shell, as is indicated by the measurements given 

 above of two of the type specimens, but in all other respects the 

 characters are quite constant. 



