252 THE CHICAGO ACADEMY OF SCIENCES. 



they soon assume the form of those in pulchella. There are 

 about 70 rows of teeth. 



Genitalia : As i n pulchella . 



Distribution: Europe, Northern Africa, Asia, North Amer- 

 ica, Australia. (Sterki.) 



Geological distribution: Pleistocene; Loess. 



Habitat: Same as pulchella. 



Remarks: This species is distinguished ivom pulchella by 

 its numerous heavy ribs and darker color. It does not seem 

 to be a common species in this area and has thus far been 

 found only in the northern and southern regions. 



101. Vallonia parvula Sterki. 



Vallonia parvula STERKI, Proc. Phil. Acad., p. 265, 1893. 



Vallonia americana ANCEY, STERKI, Proc. Phil. Acad., p. 266, 1893. 



Shell: "Small, widely umbilicated, especially for the last 

 one-third to one-half whorl, quite flat above or with very little 

 prominent apex, thin, horn-colored to nearly colorless, with 

 fine, dense, membranous ribs (about thirty to thirty-eight on 

 the last whorl), and microscopic, intercrossing lines between 

 them; nucleus with fine revolving lines; whorls a little over 

 three, slightly flattened above and below the periphery, with a 

 deep suture; the last much wider than the penultimate, rather 

 rapidly expanding toward the aperture and descending only 

 at the suture in front; aperture very oblique, tangential and 

 rather inclined, almost circular, with ends of margin much ap- 

 proximate; peristome with a rather strong, pale horn-colored 

 lip. \\ Diameter major, 2.00; min., 1.6; altitude about 0.8 m." 

 (Sterki.) 



Greater diameter, 2.00; lesser diameter, 1.40; height, 0.90 mill. (12318.) 

 2.10; " " 1.60; " 1.00 ( (12318.) 



Animal: As in costata. 



Jaw : With about eighteen ribs, otherwise as in costata. 



Radula formula: ^+i+f+i+f +i+^r (n I n); 

 the teeth are all like those of costata, the same in the number 

 of cusps on the marginals, and in the rapid transition from 

 laterals to marginals. 



Genitalia : Same as in pulchella . 



Distribution: Illinois, Iowa, Nebraska, Kansas, Indian Ter- 

 ritory. (Sterki.) Bay Island, Lake Erie. (Bryant Walker.) 



Geological distribution: Pleistocene; Loess of Mississippi 

 Valley. 



