216 THE CANADIAN NATURALIST. Vol. vi.] 



from the dorsal margin. Externally it is gently concave in the 

 ventral two-thirds of the surface ; a space around the nucleus is 

 convex, and finely striated concentrically. On the inner surface 

 there is a small pit at the dorsal third of the depth, indicating 

 the position of the nucleus. From this point radiate ten elongate 

 ovate scurs, arranged in the form of a star, the rays towards the 

 ventral side being the longest. None of these sciirs quite reach 

 the margin. 



The shell and operculum are thin and of a finely lamellar 

 structure, smooth and shining. 



Occurs at Bic and St. Simon ; also at Troy, N.Y. 



Collectors, T. C. Weston and S. W. Ford. 



Sometimes numerous small specimens from half a line to three 

 lines in length are found with the operculum on the same slab. 



This shell appears to m3 at present to constitute a new genus, 

 differing from the majority of the species of Hyolitlies in its cir- 

 cular section, the operculum not divided into dorsal and ventral 

 lines, and in the remarkable system of muscular impressions on 

 the interior. Burrande has figured an operculum of the same 

 type, differing from this in having only three instead of five pairs 

 of impressions. They are, however, arranged on the same plan 

 in both the Canadian and Bohemian species.* It is possible that 

 our species may be a Salferella. 



H. PRINCEPS. — Shell laro'e, sometimes attainins: a lens-th of 

 three or four inches, tapering at the rate of about three lines to 

 the inch. In perfectly symmetrical specimens, the transverse 

 section is nearly a semicircle, the ventral side being almost flat, 

 usually with a slight convexity, and the sides and the dorsum 

 uniformly rounded. In many of the individuals, however, one 

 side is more abruptly rounded than the other, in consequence of 

 which the median line of the dorsum is not directly over that of 

 the ventral side, and the specimen seems distorted. This is not 

 the result of pressure, but is the original form of the shell. Some- 

 times, also, there is a rounded groove along the median line of 

 the dorsum. The latter is somewhat more narrowly rounded 

 than the sides. Lower lip uniformly convex, and projecting 

 about three lines in a large specimen. Surface with fine striae 

 and sm dl sub-imbricating ridges of growth. These curve for- 

 wards on the ventral side. In passing upwards on the sides, they 



♦ Systeme Silurian, &c., vol. III., pi. 9, fig 16 H, and fig. 17. 



