192 PALAEONTOLOGY. 



lines of growtli, scarcely visible without the aid of a lens; aperture subovate, 

 rather narrowly rounded below, and acutely angular above ; columella 

 twisted into a moderately prominent fold. 



Length, 0.39 inch; breadth, 0.19 inch; apical angle slightly convex, 

 divergence about 38*^. 



This variable form is so closely allied to the last that I am nearly satisfied 

 that it is only a variety of the same. Its chief difference consists in having the 

 volutions of its spire a little more convex, and more drawn out, as it were, 

 so as to give decidedly greater obliquity to the suture. It seems to be even 

 more nearly allied to some of the more slender forms regarded by Mr. Binney 

 as varieties of L. humilis of Say; though it is a decidedly more attenuated, 

 less compact shell than that represented by Mr. Binne}'s figure of L. humilis, 

 given on p. 63 of his "Land and Fresh- Water Shells", published by the 

 Smithsonian Institution. Thei'e is scarcely any probability, however, that 

 our shell is identical with any of the existing species. 



Locality and position. — Same as last. Colonel Simpson's collection, in the 

 Museum of the Smithsonian Institution. 



LiMN^A (PoLYRUYTis) KiNGU, Meek. 



Shell ovate; spire short; volutions about four, convex, rapidly increas- 

 „. . ,, _ ing in size, last one very large and ventricose ; suture 



well defined; aperture large, subovate ; columella appar- 

 ently with a moderately well-developed fold; surface 

 ornamented by regular, distinct, vertical costae, that are 

 strongly defined on the body-volution, but more obscure 

 or nearly obsolete on the spire. 



Length, 0.73 inch; breadth, about 0.43 inch. 

 This species is remarkable for having its surface 

 ornamented by very regular, vertical costse, quite 

 strongly defined on its body-volution. . This character 

 will readily distinguish it from any other sjiecies, either recent or fossil, 

 known to me, and, with its other characters, forbid its reference to any of 

 the established subgenera. In the possession of ribs, it agrees with Pleu- 



