468 THE CANADIAN NATURALIST. [Vol. vi. 



converging to the apex, where they meet at an angle of between 

 seventy and eighty degrees. In one of the two specimena col- 

 lected, there is a flat margin on each side one-sixth the whole 

 width of the shell. Between these two flat margins the remain- 

 der of the shell is gently convex. In the other specimen this 

 central space is slightly convex in the anterior part of the shell, 

 but on approaching the beak it becomes an angular roof-shaped 

 ridge. The shell is thin, bluek and shining with obscure fluctua- 

 ting, concentric undulations of growth, and witli very line, obs- 

 curely indicated, longitudinal stritv. 

 Length nine lines; width five lines. 



LlNOtll.ELLA ? APFFNIS, SJICC. UOV. 

 Fig-. 4. 



Ventral valve elongate, conical or acutely triangular. Apical 

 angle about 45'-'. Front margin gently convex in the middle, 

 rounded at the angles ; sides nearly straight, uniformly converg- 

 ing from the anterior angles to the beak. Surface with very 

 tine longitudinal strife, about ten in the width of one line. 



This species is founded upon the single specimen of a ventral 

 valve above figured. The u{)per two-thirds is partly worn away 

 in the middle, leaving only the outline in the stone. It appears 

 to have been, when perl'ect, gently convex, the rostral j)ortion 

 near the beak semi-cylindrical. Jjcngth about thirteen lines, 

 width nine lines. 



The dorsal valve has not been identified. 



liiNdiJLELi.A? SPISSA, spec. nov. 

 Kig. n, a, b, f. 

 Shell s.-')-pentagon!il, or sul)-ovatc, length and width about 

 etiual, sometimes strongly veiitricose. Dorsal valve with the 

 front margin straight or very gently convex for about two-thirds 

 the width in the middle; antirio. .•iimlos rounded ; sides straight 

 or slightly convex and sub-parallel until within one-third or one- 

 fourth the len!j;th from the beak, then converging to the apex, 

 where they form an obtuse angle which varies fri»m 100 to about 

 110 degrees. This valve is generally very convex, sometimes 

 almost hemispherical, the outline on a side view is rather abrupt- 

 ly elevated in the rostral third, depressed convex for a short 

 space in the middle, and then more gently descending to the 

 front margin. Most ol' the specimens of this valve are eight or 

 nine lines in length, and about the same in width. 



