FOSSILS OK TIllC VVAVKIJLY OHOIIP. 259 



GASTEROPODA. 



Gemis EUOMPIIALUS Sow. 



EUOMPHALUS (Straparollfs) Utahbnsis u. sp. 



Plato IV, figs. -20-23. 



Shell of niediuin size, discoidal, composed of al)Oiit four volutions, 

 which are coiled nearly or quite in the same plane, and in close contact with 

 each other, but not embracing or overlapping, and but moderately increas- 

 ing- iu diameter with increased growth. On the upper snri'ace, the volution^^ 

 are marked, near the middle of their diameter, Ijy a narrow, sharply elevated 

 band, or carina ; within which tlie surface slopes rapidly and evenly to its 

 contact with the preceding wiiorl ; outside, of the carina, the volution is 

 evenl}^ and regularly rounded across the dorsum and to the edge of the 

 broad, open umbilicus, where there is a nearly obsolete angularity, situated 

 considerably within the middle of the volution ; within the umbilicus the 

 surface is somewhat evenly rounded. The surface of contact of each volu- 

 tion with the preceding one is very narrow and slight, leaving the inner 

 ones projecting on the sides of the shell, exposing the greater part of each 

 volution. 



Surface of the shell marked by rather distinct transverse lines of 

 growth, which are sometimes grouped so as to form slight transverse undu- 

 lations on the larger part of the shell. These lines have a slight outward 

 convexity on that portion within the carina of the upper side, and on the 

 outer portion a somewhat retral curvature as they ci-oss the body of the 

 volution. 



The species is of the type (if Eiiniuphalus peutdiijiiiJaris Sow., and 

 somewhat closely ri'sembles S. siniUis \'m\ pUuriis 31. & W. (({etd. Kept. Ills., 

 vol. ii, j)l. 19, tig. 5), but ditlers in the sharp carina of the upper siile, and in 

 having. the volutions coiled more decidedly in the same plane. This shell 

 also attains a much greater size than that one is knoAvn to do: the largest 

 specimen observed having a diameter of nearly an inch and two-thirds. 

 It is also related to S. jjlanodorsahis of the same authors (loc cif., \)\. 24, 

 fig. 2), but is readily distinguished by the form of the upper surface of the 

 volution. 



