PELECYPODA 



601 



straight; pallial line obscure; surface with radiating fringed wrinkles; 

 periostracum dirty white; length 17 min.; height 10 mm.; width 7.5 mm.: 

 Nova Scotia to Texas, in shallow water; common. 



FAMILY 3. ANATINIDAE. 



Shell thin, moie or less inequi valve, exterior often granular; hinge 

 toothless or with a spatulate lamella; ligament often with an ossicle; 

 pallial line obscure: 14 species on the Atlantic coast. 



1. THRACIA Blainville. Shell 

 nearly equivalve, gaping behind, 

 smooth; siphons rather long, sepa- 

 rate; umbo prominent; spatulate 

 process of hinge in each valve, and 

 very oblique: 26 species. 



T. conradi Couthouy (Fig. 950). 

 Shell thin, almost round, somewhat 

 elongated and truncated behind, 

 whitish in color ; ligament prominent ; 

 pallial sinus deep; periostracum thin 

 and brown; length 75 mm.; height 65 mm.; width 38 mm.: Labrador to 

 Cape Hatteras, buried deep in the sand or mud in shallow water. 



2. COCHLODESMA Couthouy. Shell oval, inequivalve, slightly gaping 

 at both ends; hinge with a spatulate process in each valve and a small 



ossicle; an internal rib extends from the hinge to 

 the posterior margin; siphons long and separate: 

 several species. 



0. leanum (Conrad) (Fig. 951). Shell oval, very 

 thin; right valve the more convex, the left valve 

 being nearly flat; length 35 mm.; height 25 mm.; 

 width 11 mm. : Nova Scotia to Cape Hatteras ; com- 

 mon in shallow water. 



Fig. 950 Thracia conradi (Gould). 



Fig. 951 



Gochlodesma leanum 

 (Gould). 



ORDER 5. SEPTIBRANCHIATA. 



Ctenidia absent, but replaced by a muscular septum (Fig. 890, D) 

 pierced by slits extending from the anterior adductor muscle to the point 

 of separation of the siphons and dividing the mantle cavity into 2 cham- 

 bers, one lying above the other : 2 families. 



FAMILY CUSPIDAEIIDAE. 



Shell small, slightly inequivalve, not pearly, much attenuated and 

 gaping behind; a spatulate cartilage process in each valve; hinge teeth 

 present or absent; pallial line shallow; mantle closed; siphons short and 

 united : about 20 species on the Atlantic coast, mostly in deep water. 



