Synopsis of the family Cardiidae and of the North American species
Proceedings of the United States National Museum
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 followingsynop.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^stematic changes, that this family is here regarded as not
... 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, Lunnocardlidce, 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 Zophocardlam. 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 posterior. The valves have serrate margins and frei^uently gape behind.