THE NAUTILUS. 81 



The apex Is very otiiuse, bein;^ almost fiat on top when viewed in 

 profile. 



IX. Ancylus shimeki Pilsbry (1890). PI. 6, fijrs. 17-19. 



1890. Ancylus obliquus Sliimek. Bull. Lab. N;it. Hisl. StHte 

 Univ. la., 1, p. 214. 



1890. Ancylus shiniekii Pilsbry. Naut., IV, p. 48. 



Shell elevated, thin, transparent, horn-colored, with a yellowish- 

 brown epidermis ; aperture ovate, conspicuously wider anteriorly, in 

 many (especially young) specimens slightly reniform by a barely 

 perceptible incurving of the right margin, the anterior, left and pos- 

 terior margins regularly rounded, the right slightly incurved, 

 straight, or but slightly convex; apex somewhat acute, elevated, 

 strongly depressed posteriorly and to the right, and curved down- 

 ward, in most specimens quite overhanging the posterior right 

 margin of the shell ; the apical portion of the shell (one-half or mote) 

 is strongly laterally, or rather obliquely, compressed, a character 

 which makes the young appear proportionately much narrower than 

 the adults ; the posterior slope of the shell is long and strongly con- 

 vex, the posterior being short and concave. The surface is marked 

 by fine lines of growth. 



Largest specimen: Length 3.5, width 1.8, height 1.2 mm. 



Average dimensions: Length 2.7, width 1.7, height 1.2 mm. — 

 (Shimek.) 



As the Bulletin, in which this species was described, is very 

 scarce and out of print, it seems better to reproduce the original de- 

 scription, which is very full and accurate, than to present a new one. 

 The only specification to be added being that the apex is radially 

 striate. 



Through the kindness of Prof. Shimek, I have before me part of 

 the original lot collected by him in Deadman's Run, near Lincoln, 

 Neb. It has also been found at Calloway, Neb., living on Cerato- 

 phylluin demersum L. In the collection of the Philadelphia Academy 

 a single immature specimen was detected in a vial of A. rivularis 

 from the Delaware River at Philadelphia (No. 75811). These are 

 the only authentic records known to me. The tentative reference of 

 this species to Gundlachia by Pilsbry (Naut., IV, p. 48, and IX, 

 p. 63), was based on a misapprehension of the species, which is 

 quite different from the Rock Island, Ills., examples figured by him. 



