SYNOPSIS OF THE FAMILY CARDTID.F: AND OF THE 

 NORTH AMERICAN SPECIES. 



By William Healey Dall, 



Honorary Curator, D'lvmon of MoUusks. 



In pursuance of the plan already carried out for th(^ Mactracea, 

 Diplodontida\ Leptonacea, Psanimobiidiv, Solenidte, and Tellinidaj, 

 I have prepared the following- synop.sis of the CardU.dw^ to include 

 the species found on both coasts of North America, as well as the 

 subdivisions of the family considered as a whole. I should perhaps 

 explain, for the benefit of students who have not followed recent S3^s- 

 tematic changes, that this family is here regarded as not including 

 the curious brackish- water forms associated with Adacna in the 

 waters of the Caspian and the Tertiary horizons of southeastern 

 Europe. These forms were separated as a distinct family, Lunnocar- 

 dlidce, by Stoliczka in 1870. 



The forms included in the present paper have the hinge teeth arched 

 (Cyclodont), springing from below the hinge margin, with th(» hinge 

 plate obscure or undeveloped, and in many cases the two cardinal 

 teeth in one of the valves rotated so .that one stands above the other, 

 while in the opposite valve one precedes the other horizontally, so 

 that the axes of the two pairs when the shell is closed cross each other 

 nearly at right angles. There is a small and a large cardinal in each 

 valve; when the shell is closed the two small cardinals are external to 

 the large ones. The laterals are present in all except Zophocard lam. 

 The sculpture of the shell is chiefly radial, the lobes of the mantle 

 free below the siphons, the foot geniculate, elongated, and rounded, 

 except in Serripei-:, which has it compressed and serrnte l)elow. The 

 gills have a very simple type of reticulation, strongly plicate; the 

 anal chamber in some cases is separated from the pedal by a siphonal 

 septum. The ligament and resilium are parivincular, external and pos- 

 terior. The valves have serrate margins and frei^uently gape behind. 



Proceedings U. S. National Museum, Vol. XXlll, No. 1214. 



381 



