WHITE ON NEW INVEETEBRATES. 717 



bly enlarged, composing much tbe greater part of the shell, almost or 

 quite regularly rounded from the suture to the umbilicus ; suture well 

 defined, and rendered still more conspicuous by the convexity of the 

 volutions; umbilicus very small and deep; aperture short, subovate or 

 subcircular, obtusely angular at its distal side ; a little straightened by 

 contact with the next volution between that angle and the umbilicus, 

 and elsewhere almost regularly rounded. 



Surface smooth, almost polished, but marked by very fine lines of 

 growth. 



Length from front to apex 18 millimeters; breadth of body-volution 

 18 millimeters. 



This shell is proportionally shorter than any other species of the 

 genus known to me, but it seems to possess all the characteristics of 

 Viviparus. Its outer lip has the usual straight margin, but its umbili- 

 cus is a little more open than usual, and the inner lip not reflexed, but 

 almost continuous in its curvature with the outer lip. 



Fosition and locality. — Laramie Group, Crow Creek, Colorado, 10 miles 

 above its confluence with South Platte Eiver, Northern Colorado. 



Viviparus coucsi (sp. nov.). 



Shell very large when fully adult ; volutions six or seven, convex, the 

 distal side of the last one especially rounded abruptly in to the suture, 

 giving it a somewhat shouldered aspect there, while the outer side is 

 broadly convex and sloping gently forward and inward ; suture deeply 

 impressed, the apparent depth being increased by the great convexity 

 of the volutions. Surface marked by the ordinary lines of growth, no 

 revolving marks of any kind being detected. The lines of growth indi- 

 cate that the margin of the outer lip was nearly straight, as is usual 

 with species of this genus, and which character distinguishes it from 

 Campeloma. Inner lip thickened, and reflexed at the proximal or ante- 

 rior end, but not covering the umbilical fissure there, which is moder- 

 ately large. The precise shape of the aperture is unknown, but it is 

 probably ovate. 



No entirely perfect examples have been discovered, but the largest 

 one yet obtained would, if perfect, measure about 65 millimeters in 

 length ; fall width of body-volution 38 millimeters. 



This species is described by Meek in vol. iv, p. 181, pi. 17, fig. 15, King's 

 United States Geological Survey of the Fortieth Parallel, and referred 

 to the genus Campeloma, but not specifically named. The numerous 

 specimens, however, that have been obtained from the typical and other 

 localities show that the species possesses the true characters of Viviparus. 



This species is distinguished from all others of the genus known to 

 me in American strata by its great size, and there are few other species 

 with which it is in any danger of being confounded. From V. paludinw- 

 formis Hall, it differs in its more robust form, in the greater convexity 

 of its volutions and the abrupt rounding of their distal side, and in the 

 presence of a comparatively large umbilical fissure. 



