338 Loiver Silurian Fauna of Minnesota. 



height of the cast are as 8, 6 and 3. Greatest elevation central. Beak of 

 half the elevation, obtuse, and near the posterior margin. Surface marked 

 by several concentric varices of growth. No radiating marks are visible 

 on the cast. Two large round muscle scars have been made out and in- 

 dications of a third are present, all on the same side. 



The specimen figured is from the Orthisina bed at Kenyon, Good- 

 hue county, Minn. 



CYPRICARDITES LUCULENTUS n. Sp. 



Plate VI, figures 25 and 26. 



Shell about 35 mm. long, and about same in width; convexity about 

 20 mm. Hinge nearly straight, anterior margin rounded above and then 

 nearly straight from thence to a point on the ventral margin directly be- 

 low the beaks. Thence the curvature is stronger up to the hinge. The 

 beaks are oppressed and coiled in and forward; the umbones are large, 

 and have a strong convexity that extends to the ventral and posterior 

 margin. In front and back of this convexity the surface is depressed, or 

 a little concave. 



The muscle scars are large, the anterior one is situated close to the 

 hinge and the anterior margin ; the posterior scar is the larger, is close to 

 the palial line, and about half its diameter below the hinge. Cardinal 

 teeth two; the lateral teeth have not been clearly made out, but are prob- 

 ably small and few, ligament external. Casts have an elevated ridge ex- 

 tending from the beak towards the ventral margin. 



From the Limestone of the Cincinnati group, town of Bristol, Fill- 

 more county, Minnesota. 



CYPRICARDITES MINNESOTENSIS n, Sp. 



Plate VI, figure 21. 



Form ovate with the apex at the antero-dorsal margin ; length 30 mm., 

 breadth 25 mm. ; convexity moderate and uniform. Beak small, acute, in- 

 curved, with two small cardinal teeth and two larger curved postero-lateral 

 teeth. Two muscle scars ; the anterior one small and close to the margin ; 

 posterior scar large, indistinctly outlined, remote from the hinge and from 

 the posterior margin. Palial line simple and deep. The specimen fig- 

 ured is a cast of a left valve. Rare. 



From the crystalline slabs of the Stictoporella bed at Minneapolis. 



CYPRICARDITES TRIANGULARIS n. Sp. 



Plate VI, figure 23, 



Compare Cypricardites (Ambonychia) obtusa Hall. 



Cast small, narrow anteriorly. Hinge straight and about two-thirds 

 as long as the cast. The anterior margin is slightly curving and forms an 

 angle of 75 degrees with the hinge line. The posterior and ventral mar- 

 gins together form a semicircle, with a diameter equal to the width of the 

 shell. Beaks anterior, nearly straight, flattened laterally, directed for- 

 ward, and projecting. Anterior muscle scar large and reniform. Posterior 



