No. 89.] 89 



TEREBRATULA LENS (n.s.). 



Shell ovate, broadly elliptical or lenticular below, and abruptly tapering towards 

 the beak, the greatest width a little below the middle, moderately gibbous : 

 valves subequally convex, the width about four-fifths as great as the length, 

 and the depth equal to about half the length. Ventral valve less convex than 

 the dorsal, the beak moderatel}'- incurved and broadly truncated, the lateral 

 slopes subangular; without visible sinus or elevation. Dorsal valve broadly 

 elliptical or subcircular, a little more convex than the opposite. Surface marked 

 by indistinct lines of growth : shell structure punctate. Length nearly seven- 

 tenths, and breadth six-tenths of an inch. 



This species is proportionally shorter and broader, and more abruptly tapering 

 to the beak, than either of the preceding species. It varies little in length from the 

 larger specimens of T. lincklani; but that species is narrower, and the valves 

 more gibbous. The T. rectirostra is a more elongate shell, attains a length of an 

 inch or more, and has nearly straight sides from the middle to the beak. 



Geological formation and locality. In the Upper Helderberg limeston : at 

 Clarence hollow, Erie county. Collected by Col. Jewbtt. 



TEREBRATULA PLANIROSTRA (n.s). 



Shell subangularly ovate, unequally subquadrilateral : the front often truncate, 

 giving a subpentagonal outline; greatest width near the middle of the shell; 

 width and length about as six to seven : the thickness at the greatest convexity 

 of the two valves is more than half the length. Ventral valve with the greatest 

 convexity above the middle, the lower part flattened or depressed along the 

 centre : beak moderately incurved and truncate at the extremity, depressed or 

 flattened on the umbo; lateral slopes angular; deltidial pieces large. Dorsal 

 valve shorter than the opposite, very convex and often extremely gibbous above 

 the middle, more or less flattened towards the front. Surface ( in old shells) 

 marked by strong lines of growth, which are sometimes regularly and evenly 

 disposed as concentric laminae, often roughened : shell structure punctate. 

 Length of full-grown individuals about one inch. 

 This fossil, in full-grown specimens, is distinguished by a subangular fovm and 



a truncation in front : an incipient sinus marks the ventral valve. The flattening 



of the umbo, and angular margins of the lateral slopes of the ventral valve, are 



distinctive features. 



Geological formation and locality. In the shales of the Hamilton group : at 



York, Moscow and Geneseoin Livingston county, and in Ontario county, N.York. 

 For the finest specimen which I have seen, I am indebted to Prof. E. N. HoRS- 



FOED of Cambridge, who collected it many years since at Moscow. 



The preceding species are referred to Terebratula, from their general form and 



punctate structure. The internal arrangement is unknown; and it is possible that 



they may prove distinct from that genus, when we become acquainted with the 



interior structure. 



ATHYRIS VITTATA ( n. s.). 

 Shell subquadrilateral, usually a little transverse, trilobate from the strong 

 mesial sinus and elevation : hinge-line extending more than half the width of 

 the shell; cardinal extremities rounded; length and breadth as five to six. Ven- 

 tral valve most convex above the middle, the sinus often reaching to the beak 

 and becoming sharply defined below the middle of the valve, elevating the front 

 in a defined semicircular arch; sides of the valve regularly curving to the mar- 

 gins. Dorsal valve usujiUy a little the more gibbous, the greatest convexity above 

 [Senate, No. 89.] U 



