Q^^ PROCEEDINGS OF THE ACADEMY OF [NoV.j 



The living species are largely shallow water forms, especially 

 the byssiferous types, but some of the minute species occur at con- 

 siderable depths; the Arctic type, Cydocardla, occurs in 822 

 fathoms (1,707 meters), and Cali/ptogena in 322 fathoms (669 

 meters). 



In America Cardita s.s. and Venericardia s.s., Miodon, Calyp- 

 togena, Milneria and Carditella are restricted to the Pacific coast ; 

 while Pleuromeris and Pteromeris are known, so far, only from the 

 Atlantic. The Pacific coast has twenty -seven and the Atlantic 

 coast only twelve species of Carditacea, Carditamera with seven 

 and Gyclocardia with fifteen being the most prolific in species. 



Of those enumerated in this paper seven are new. It seems that 

 the world musters, as a whole, only about sixty species; the two 

 Americas thirty-nine, and the Pacific coast nearly half of all that 

 are known. 



The Carditacea are divided into Carditidce, with the ligament 

 and resilium external and united, and Condi/locardiidce, with the 

 resilium immersed and the hinge in a more or less permanently 

 imperfectly developed state. 



The Carditidce comprise two subfamilies: Cardiiinoe, with the 

 marsupium dorsal, or superior, and not reflected in the structure of 

 the valves; and Theealiince, with the marsupium ventral, or infe- 

 rior, and protected by an infolding or indentation of the inner 

 shelly layer of the valves. The subdivisions of these groups are as 

 follows : 



Subfamily OARDITIN^. 

 Genus CAEDITA (Bruguiere, 1792), Lamarck, 1799. 



Type Chama calyculata Linne' (+ Mytilicardita Anton, 1839; 

 Mytilicardia Herrm., 1847). 



Valves elongate-quadrate, strongly radially ribbed, very inequi- 

 lateral and with a narrow byssal gape. 



Section Cardita s.s. 



Hinge with two left and three right cardinals, the laterals obso 

 lete in the adult. 



Sectiou Carditamera Conrad, 1838. 

 Type Cardita araia Conrad. 

 Valves with the laterals well developed in tiie adult, the right 



