306 THE CHICAGO ACADEMY OF SCIENCES. 



parts; aperture as large as the shell, rounded; peristome sim- 

 ple, entire, acute; color greenish-horn. 



Length, 6.00; width, 4.00; height, 3.00 mill. 



Animal: Not examined. 



yaw: Not examined. 



Radida: Not examined. 



Genitalia: Not examined. 



Distribution: Same as rivularis. 



Geological distribution : Pleistocene. 



Habitat: Similar to rivularis. 



Remarks: This species is wider and more conical than 

 rivularis, and the apex is more central and not directed later- 

 ally. It seems to be very rare and has been found only in the 

 DuPage River. 



124. Ancylus shimekii Pilsbry, pi. xxxi, figs. 9, 10. 



Ancylus obliquus, SHIMEK, Bull. Lab. Nat. Hist. Univ. of Iowa, Vol. I, 



Nos. 3-4, p. 214, pi. iii, figs. 5 , 5*> , 5c , 1890. (Preoccupied.) 

 Ancylus shimekii PILSBRY, The Nautilus, Vol. IV, p. 48, 1890. 



"Shell: Elevated, thin, transparent, horn-colored, with a 

 yellowish-brown epidermis; aperture ovate, conspicuously wider 

 anteriorly, in many (especially young) specimens slightly reni- 

 form by a barely perceptible incurving of the right margin, 

 the anterior, left and posterior margins regularly rounded, the 

 right slightly incurved, straight, or but slightly convex; apex 

 somewhat acute, elevated, strongly deflected posteriorly and 

 to the right, and curved downward, in most specimens quite 

 overhanging the posterior right margin of the shell; the apical 

 portion of the shell (one-half or more) is strongly laterally, or 

 rather, obliquely, compressed, a character which makes the 

 young appear proportionally much narrower than the adults; 

 the anterior slope of the shell is long and strongly convex, the 

 posterior being short and concave. The surface is marked by 

 fine lines of growth." (Shimek.) 



Length,3.50; width, 1.80; height, 1.50 mill. (Shimek.) Large specimen. 



" 2.70; " 1.70; " 1.20 " (Shimek.) Average measurement. 

 " 3.10; " 1.70; " 1.10 " Joliet specimen. 



Animal: "Uniform bluish-white color; the foot is ovate, 

 wider anteriorly, and rather narrow for an Ancylus." (Shimek.) 



Radula: "Rather narrow, the dental formula being 12-1- 

 12." (Shimek.) 



Distribution: Five miles east of Lincoln, Neb., in Dead 



