MUSEUM OF COMPARATIVE ZOOLOGY. 63 



Strophomena alterniradiata Shalek. 



JShell semi-oval ; width at hinge-line about three eighths greater than from 

 beak to border. Toothed valve distinctly convex near the umbo ; remainder 

 of valve flattened or slightly concave. Socket-valve slightly concave just 

 below the umbo, slightly convex over the remainder of the surface. Sur- 

 face of both valves with distinct rounded radii, one half of which originate 

 at the beak, the others coming in by implantation at the border of the um- 

 bonal third of the valves; intervals very wide. Hinge area of toothed 

 valve wide, — one line in specimens ten lines broad ; that of socket-valve 

 narrow, nearly linear. Fissure wider than high; teeth small ami pointed. 

 Brachial supports oblique, meeting at an angle of 90°. Cardinal process 

 very small, slightly projecting. — Southwest Point, Anticosti. 



Brachyprion Shaler. 



Dental plates transversely much elongated ; scarcely distinct from the 

 remainder of the hinge-line; vertically serrated. 

 Type. — Strophomena leda Billings. 



Brachyprion leda Shaler. 



Syn. Strophomena leda Billings. — Near Becscie Biver Bay. 



Brachyprion ventricosum Shaler. 



Syx. Strophomena Philomela Billings ? 



Sub-trigonal margin opposite the hinge-line rounded, strongly alate, one 

 side being unusually more prolonged than the other; hinge-line two fifths 

 longer than distance from beak to border ; width on hinge-line, 2.30 inches ; at 

 one third the distance from beak to border, 1.33 inches; convexity of toothed 

 valve equal to one third the distance from beak to border. Toothed valve 

 strongly evenly convex, much compressed near the alations ; highest point 

 two thirds the distance from beak to border ; hinge area narrow ; fissure very 

 small, triangular, not extending to the beak. Area of socket-valve narrow, 

 cardinal process small. Surface covered with very fine linear radial strise 

 of two sizes, four or five of the smaller between each pair of larger ; 

 smaller striae nearly microscopic ; several indistinct concentric undulations 

 near the hinge-line. — Near Southwest Point, Anticosti. Division E, Can- 

 ada Geological Survey. 



Brachyprion geniculatnm Shaler. 



Shell semi-elliptical or sub-trigonal ; greatest width at hinge-line : hinge- 

 line straight ; about one third greater than from beak to border. Socket- 

 valve plane or slightly concave over the visceral disk, suddenly deflected at 

 two thirds the distance from beak to border. Surface of shell with a number 

 of rounded radial strife (twenty to fifty). Those on the centre much larger 

 than those on the sides ; between each pair from five to nine very fine 



