NO. 1312. SYNOPSIS OF THE VENERID.E—DALL. 361 



Shell trigonal, tumid, with a keeled escutcheon and short, rounded 

 pallial sinus. 



This is otherwise essentially like the preceding section, but owing to 

 the different form appears very distinct. It is not Ilemitapes of 

 Stoliczka, Trj^on, and Fischer. 



Section Venerella Cossniann, 1886. Type, Venm hermonvillensis 

 Deshayes. Eocene. 



Shell small, ovate, concentrically striate; lunule large, circumscribed, 

 escutcheon not defined; internal margins smooth; pallial sinus small 

 free, ascending, rounded in front; three cardinal teeth in each valve, 

 the margin of the hinge plate excavated at the interspaces; posterior 

 right cardinal long, bifid; the other teeth entire. 



These forms are distinguished from the smaller species of Katelysia 

 chiefly by the form and disposition of the teeth. 



Section Mercimonia Dall, 1902. Type, Yenim Bernayi Cossraann. 

 Eocene. 



Shell small, ovate, concentrically striate, rather tumid; hinge nor- 

 mal, the posterior left cardinal slender, not elongated; posterior right 

 cardinal grooved; margins entire; the pallial sinus nearly obsolete. 



This is Mercenaria Cossmann, 1880, not of Schumacher, 1817. The 

 species included in Cossmann's list which possess a small but deep 

 pallial sinus might be referred to Venerella^ from which they hardl}^ 

 difier. 



Section Textivenus Cossmann, 1886. T5''pe, Venus texta Lamarck. 

 Eocene. 



Shell ovate, convex, sculptured by fine obliquely reticulate or 

 divaricate subequal threadlike ridges; lunule small, circumscribed, 

 escutcheon bordered by a radial ridge; internal margins smooth, 

 pallial sinus small, angular, free; three cardinals in each valve, the 

 right posterior cardinal broadly bifid ; the right posterior dorsal mar- 

 gin ])ehind the hinge plate grooved to receive the edge of the opposite 

 valve. 



Section Samarangla Dall, 1902. Type, Venus qtiadrangularis Adams 

 and Reeve. 



Shell rounded-quadrate, subcom pressed, white, with a dull surface; 

 sculpture of concentric striation, more forcible distally; internal mar- 

 gins smooth; lunule unevenly divided between the valves, smaller in 

 the right valve; escutcheon not defined; pallial sinus moderate, angu- 

 lar in front, free below; three cardinals in each valve, the middle left 

 and two posterior right cardinals bitid; hinge strong. 



The species belonging to this group are.massiA'e and solid. V. h')i- 

 ticmlarls Sowerb}" is an exam})le. The anterior left and posterior 

 right dorsal margins are grooved behind the hingeplate to receive the 

 beveled edges of the opi)osite valve. 



