696 PROCEEDINGS OF THE ACADEMY OF [N( 



SYNOPSIS OF THE CARDITACEA AND OF THE AMERICAN SPECIES. 

 BY WILLIAM HEALEY DALL. 



This paper is in continuation of the series of similar synopses of 

 groups of bivalve shells which the writer has prepared during the 

 last few years, including the Leptonacea, TelUnacea, Veneracea, 

 Lucinacea, Cardiacea, etc. The present paper contains a summary 

 of the groups included in the Carditidce and the Condylocardiidce, 

 and of the species reported to inhabit the Atlantic and Pacific 

 coasts of America. Doubtless with a better exploration of the 

 tropical and South American waters some additions may be ex- 

 pected to the list. 



The group is intimately related to the Crassatellitidce, Astartidce 

 and Chamidce, as shown by its paleontologic history, anatomy and 

 development. There are no siphons, the border of the mantle is 

 pierced for the excurrent orifice, while the incurrent orifice may or 

 may not be complete, but in most cases seems to be formed by the 

 apposition rather than the organic connection, ventrally, of the 

 edges of the mantle. The gills are coarsely reticular and usually 

 united behind the foot. In many, if not all, cases the young are 

 developed within the body cavity of the mother and retained there 

 until some progress in secreting the nepionic shell has been made, in 

 addition to the completion of the prodissoconch. This incubation 

 in one group takes place in the atrium of the ovary, in another in 

 a specially developed fold of the ventral part of the mantle lobes 

 which secretes and lines a shelly marsupium which is absent in the 

 shells of male individuals. 



The species are iLsually sedentary, and mostly secrete a byssus by 

 which they fix themselves when young, and in one large group this 

 condition continues through life. The sculpture is predominantly 

 radial and often strong, the periostracum conspicuous and fre- 

 quently pilose; the valves, except in abyssal and minute species, 

 are usually solid and heavy and their margins strongly crenate. 

 The ligament in the Carditidce is strong and wholly external ; in 



