700 PROCEEDINGS OF THE ACADEMY OF [NoV., 



Section Cardites s.s. 

 Shell with external coloration, frequenting the warmer seas. 

 Section Cyclocardia Conrad, 1867. 



Type Cardita borealis Conrad. 



Shell white, with a rude periostracum j frequenting the boreal 

 seas or cold abysses. Arclurus (xray, 1839, not Cuvier, 1829; 

 Adinoholus Morse, 1869, and Scalaricardita Sacco, 1899, are syn- 

 onymous. 



Subgenus PLETJROMERIS Conrad, 1867. 



Type Cardita tridentata Say, not Reeve. 



Shell small, subtriangular, subequilateral, the hinge like Veneri- 

 cardia, but the anterior and posterior right cardinals feeble, the 

 left valve with feeble anterior and posterior laterals. 



Subgenus PTEROMERIS Conrad, 1862. 

 Type Astarte perjilana Conrad. 



Shell small, high, oblique, with narrow umbones, radial ribbing, 

 a well-marked lunule and escutcheon, the hinge as in Cardites. 

 Coripia De Gregorio, 1885, is synonymous. 



Subgenus MIODON Carpenter, 1864 (not of Sandberger, 1870). 



Type M. prolongatus Carpenter. 



Shell not very different from Pteromeris, but not compressed, 

 and with the posterior (instead of the anterior) right cardinal 

 absent and a posterior right and anterior left lateral developed 

 feebly. 



Subgenus NEOCARDIA Sowerby, 1892. 



Type N, angulata Sowerby, South Africa. 



Shell small, wing-shaped, resembling Pteromeris. Hinge as in 

 Cardites except that long posterior laterals are said to be present, 

 with no anterior laterals, the cardinals diminutive. 



Genus CALYPTOGENA Dall, 1891. 



Type C. pacifica Dall. Pliocene and Recent. 



Shell large, oblong, chalky, with only faint concentric sculpture, 

 a well-marked escutcheon, but no lunule, the inner margins 

 smooth, an anterior lateral in each valve; hinge formula ttVIItV,- 



