73 



apex obtuse, slightly angular in the ventral and broadly rounded in the 

 dorsal valve. In perfect specimens both valves are moderately convex, 

 most elevated in the upper half, especially along the middle, for a short 

 distance from the beak, about one-fourth of the width next the margin on 

 each side of the umbones compressed. Surface vrith fine concentric striae, 

 from eight to ten in the width of one line. 



Length from 15 to 18 hues ; width from 10 to 12 lines. 



The above description relates to the specimens collected in the black 

 graptolitic slates at the water's edge, a short distance below the ferry at 

 Point L^vis ; but in the thin-bedded limestones interstratified in the slates 

 on the road-side near the ferry-landing, others were collected of a smaller 

 size, but with precisely the same form and proportions. The largest found 

 at this locality is 12 lines in length and 8 lines in width. Numerous 

 smaller ones, from 3 to 10 lines in length, occur along with the larger, in 

 the same beds. At present I believe all of these belong to the same 

 species ; but should a separation hereafter be deemed advisable, it is 

 proposed to retain the name L. Quebecensis for the larger form, which is 

 associated with the graptoUtes. 



This species resembles L. quadrata, but is more nearly oval, and 

 proportionally not so broad. 



Locality and Formation. — Point L^vis. In the graptoUtic slates and 

 thin-bedded limestones of the Quebec group. 



Collector. — J. Richardson. 



Leptjena sordida. (N. sp.) 



Fig. 66. Fig. 67. 



Fig. 66. — LeptiBna sordida. — a, Ventral and 6, dorsal aspects. 



67. — L decipiens. — a, Ventral and b, dorsal aspects ; c, interior of 



dorsal valve. 



Description. — Shell smaU, obtusely semi-oval ; length equal to about 

 five-sixths of the width; cardinal angles either rounded or shghtly 

 projecting ; sides either straight or shghtly convex, and either parallel or 

 only very slightly converging in the upper half of the shell ; front half 

 broadly and uniformly rounded. 



Ventral valve strongly and uniformly convex, or depressed hemispheri- 

 cal ; a small portion at the cardinal angles compressed. Area very large, 

 forming an obtuse angle with the plane of the lateral margin. 



