252 THE CHICAGO ACADEMY OF SCIENCES. 
they soon assume the form of those in pulchella. There are 
about 70 rows of teeth. 
Genitalia: As in pulchella. 
Distribution: Europe, Northern Africa, Asia, North Amer- 
ica, Australia. (Sterki.) 
Geological distribution: Pleistocene; Loess. 
Habitat: Same as pulchella. 
Remarks: This species is distinguished from 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.4; 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.) 
ie “ BAD eH ‘ 1.60; Or L005 a PZB LBD 
Animal: As in costata. 
Jaw: Withabout eighteen ribs, otherwise as in costata. 
Radula formula: 725+4+3+44+34+444'5 (1I—I—I11); 
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. 
Genitaha: Same as in pulchella. 
Distribution: Wllinois, lowa, Nebraska, Kansas, Indian Ter- 
ritory. (Sterki.) Bay Island, Lake Erie. (Bryant Walker.) 
Geological distribution: Pleistocene; Loess of Mississippi 
Valley. 
