Silurian Fossils of Canada, 55 



Strophomena Leda. N. s. 



Fig. 2. Fig. 3. 



Fig. 2.—Stropho7nena Leda with a portion of the hinge area of the ven- 

 tral valve enlarged to shew the striated teeth. 

 3. — A specimen without ears supposed to be of the same species. 



Description, — Shell rather small and thin, semi-oval, the front 

 and front angles regularly rounded, sometimes a little narrower 

 at the base of the ears than at one third the length from the 

 hinge line, the latter usually exceeding the greatest width of the 

 shell, and forming projecting spiniform ears. Width excluding 

 the ears, five to nine lines ; length five-sixths of the width ; ears 

 one line and a half in length each, in a well preserved specimen 

 five lines wide. 



The ventral valve is in the small specimens, depressed convex 

 and nearly uniformly arched from beak to front ; the umbo well 

 defined, but the concave depressions on each side rather obscure ; 

 no deflected margin. The large specimens (nine lines wide) are 

 sometimes strongly convex. Dorsal valve concave, its curvature 

 corresponding to that of the ventral valve. Surface as in S. alter- 

 nata. 



Area of ventral valve half a in line height in a specimen seven 

 lines wide, lying nearly in the plane of the margin, apparently a 

 little sloping outwards, forming an angle of about 100° with that 

 of the dorsal valve, which latter is scarcely one-fourth of a line 

 wide. Foramen not distinctly observed but apparently wider than 

 high. 



The detached and empty ventral valves exhibit two rather 

 large triangular hinge teeth, one on each side of the foramen, 

 covered with stri£e on the outside in a manner similar to that of 

 the area of those species to which Professor Hall has given the 

 generic name of Strophodonta. 



The spiniform ears are often either broken or worn away. 



Varieties. — Several specimens nine lines wide without ears, 

 and others of the same size strongly convex, and with an indis- 



