INVERTEBRATE PALEONTOLOGY. 565 



the entire shell shorter in proportion to the breadth of Hie body-whorl. It 

 is also a rather decidedly thinner shell. 



Locality and position. — Same formation as last, at the mouth of Judith 

 River, Montana. 



Go 11 iobasis Nebrasceiisis, M. & H. 



Plate 43, tigs. 12, a-h. 

 Melania Nebrascensis, Meek and Hayden (1856), Proceed. Acad. Nat. Sci. Philad., VIII, 124. 



Shell conical-subovate ; spire moderately prom- Fig. 73. 



inent, acute, and not eroded at the apex ; volutions 

 about six, compressed-convex, last one comparatively 

 large and prominent, but not angular around the middle • 

 suture well defined ; surface marked by fine, more or 

 less distinct, lines of growth, crossed by numerous small Goniohasis Nebrasceime. 



, . t 1 • 1 11 i . Showing more accurately 



revolving lines, which vary m their size and prominence the form of the al , erture . 

 on different specimens, but are generally largest near as wel1 as tbe g eneral out - 



1 J line, than figure 12, h, of 



the middle of \ he whorls of the spire, where one of them plate 4:?. 

 is sometimes larger than the others; aperture ovate, angular above, mod- 

 erately produced and rather narrowly rounded, or obtusely subangular and 

 faintly sinuous below, a little straighter on the inner than the outer side; 

 outer lip slightly sinuous above the middle ; inner lip reflexed, and moder- 

 ately arched, sometimes scarcely covering a minute umbilical slit. 



Length, about 1 inch ; breadth, 0.52 inch ; length of aperture, 0.36 

 inch ; breadth of same, 0.23 inch ; apical angle convex, or nearly regular, 

 divergence varying with age from 50° to 37°. 



Mature specimens of this species have the spire proportionally more 

 elevated, the whorls less convex, and the aperture comparatively smaller than 

 young individuals. It also varies much in the surface-markings, even on 

 specimens of the same size. Sometimes the revolving lines are quite distinct 

 on all parts of the surface, and a few of them near the middle of the whorls 

 become more prominent than the others, while in other instances all these 

 lines are very faintly marked or even entirely obsolete. In some old spe- 

 cimens, the inner lip is a little thickened and slightly prominent, so as to 

 leave a small umbilical crevice, though not a distinct perforation, while in 

 most cases this lip is closely reflexed upon the columella. 



This shell will be readily distinguished from the last by its proportion- 



