932 THE PALEONTOLOGY OF MINNESOTA. 



LRaphlstoinldu'. 



curves; passing over the acute edge they turn strongly forward and finally back 

 again into the umbilicus. Types, E. staminea and planistriata Hall. 



RAPHISTOMINA, n. gen. Shell lenticular to depressed conical, umbilicated; 

 volutions sharply angular and carinate at the periphery, the carina projecting over 

 the but slightly impressed sutures; aperture very little oblique, subrhomboidal; 

 upper lip directed backward with a gently sigmoid curve, the sutural half convex, 

 the outer half concave, the extreme outer angle slightly hooked; outline of lower 

 lip varying from concave to convex, in the latter being almost parallel with the 

 upper; lines of growth moderately distinct, not interrupted on the upper side of the 

 whorls. Type, Raphistoma lapicida Salter. 



EUOMPHALOPTERDS, F. Roemer, 1876.* Shell trochoid or subturbinate, broadly 

 umbilicated, consisting of six or seven volutions rounded in section internally; 

 carina thin, very wide, placed between the middle and the base of the whorls, 

 enclosing numerous small tubular spaces running obliquely forward and outward 

 and somewhat at variance with the lines of growth, and opening along its outer 

 edge; aperture rounded, very oblique, the lower lip deeply and broadly sinuate; the 

 lines of growth make a sigmoid curve between the umbilicus and the outer edge of 

 the carina, the extent of the outer curve varying with the species and depending 

 upon the width of the carina; on the upper side of the whorls they are curved less 

 strongly and on the inner part in an opposite direction from that observed on the 

 base, the result being that in a species like E. undulans Lindstrom sp., in which the 

 carina is comparatively narrow, the anterior edge of the aperture, as viewed from 

 above, is a gentle sigmoid, while in a widely carinated form like E. alatus the edge 

 is biconvex, being recurved at the outer extremity. Type, E. alatus Wahlenberg sp. 



OMOSPIRA, n. gen. Shell somewhat elongate turbinate, subturriculate; volutions 

 seven or eight, ventricose, obliquely flattened in the upper part by an obtuse 

 shoulder-like angulation; the latter, which may or may not constitute the periphery 

 of the whorls, forms the outer margin of a wide band-like space in which the lines 

 of growth, which first curve strongly backward in their course from the suture line, 

 are turned in the opposite direction; a short distance before reaching the angle the 

 curve is sharpened; as in Raphistoma the junction between the two curves is marked 

 by a thin line, while beneath the outer angle the lines of growth are turned some- 

 what gently forward. Aperture somewhat quadrate-triangular, its hight "slightly 

 greater than the width, narrowly rounded but not effuse below; columellar lip 

 rather straight, not thick, usually reflexed so as to hide a minute umbilical perfora- 

 tion. Surface markings consisting of fine lines of growth only. Type, 0. laticincta, 

 n. sp. (Ulrich.) 



I., th. Ueogn.. Ed. 4, pt. 1. pi. xiv, fig 0. 



