The Saint Peter Sandstone. 71 



convexity is central. Anterior muscle sear prominent. Surface of the cast 

 is concentrically marked by growth lines which appear to show the ventral 

 margin a little more convex than on the figure. The only specimen found 

 is a little compressed, and moreover does not show clearly but that it may 

 be a modiolopsis. 

 Highland Park. 



Cypricardites dignus n. sp. 

 Plate II, figures 4 and 5. 



Shell rhomboidal, with the ventral margin longest; length of the 

 largest specimen 18 mm, bredth 12 mm. Beaks anterior, tumid, close 

 together. The hinge line is equal to about two-thirds the length of the 

 shell, is curved and apparently continuous with the anterior margin. In 

 general direction the anterior margin is vertical, but forms a strong even 

 curve, which same is continued, but less strongly, through the ventral 

 margin to the postero-ventral angle. The dorsal margin is more distinctly 

 marked off but is gently curved. The point of greatest convexity is 

 between the umbones and the centre of the shell along the rounded 

 umbonal ridge which extends from behind the beaks obliquely back to the 

 postero-ventral angle. Anterior to this umbonal ridge the shell is evenly 

 and strongly convex, but between it and the dorsal and posterior margins 

 the surface is concave. In general the specimens resemble Nuculites inflatus 

 Emmous' Geo. Rep. N. Y., p. 395, fig. 2, but have a more prominent anterior 

 margin and less produced hinge posteriorally^. Edmondia subtruncata 

 Hall Pal. N. Y., Vol. i, p. 156, and plate 34, fig. 9, (not plate 35, fig. 3, c.) 

 is very much like the specimens from the Saint Peter but is larger and 

 proportionally longer. 



South Saint Paul. 



Genus Modiolopsis. 

 Modiolopsis fountainensis n. sp. 

 Plate IV, figure 7. 

 The few specimens secured resemble Modiolopsis plana Hall, of the 

 Trenton limestone which lies upon the Saint Peter sandstone. The Saint 

 Peter specimens are larger casts, however, and have the beaks situated 

 further back and erect instead of directed forward. The convexity of the 

 shell was not strong but there was a broad deepening between the beaks 

 and the lower posterior curve of the margin, accompanied by a straighten- 

 ing of the ventral margin. The anterior muscle scar is large and close to 

 the anterior margin. The specimens were found with Lingala morsii N. H. 

 W. at the top of the Saint Peter formation (see pi. iv, fig. 9, c.) below 

 Fountain, Minn. 



Modiolopsis postica n. sp. 



Plate IV, figure 8. 



Shell about 50 mm. long, width greatest across the posterior half (30 



mm.) The hinge line is nearly straight. The beak, of the left valve here 



described, is obtuse, broad and close down to the hinge. The umbo is high 



