256 THE CHICAGO ACADEMY OF SCIENCES. 
are five and one-half whorls; the aperture is just one-third the 
length of the shell, instead of over one-third, and the surface 
is “regularly and very distinctly striated.” 
Length, 1.75; width, 0.75; aperture length, 0.50; width, 0.25 mill. (12474.) 
Animal: Faw and Dentition apparently as in C. exiguum. 
Genitalia: Not examined. 
Distribution: Evidently the same as exiguum. 
Geological distribution: Pleistocene; Loess. 
Habitat: Same as and associated with C. exiguum. 
Remarks: Exile is not as common as eazguum, the ratio 
being about 3 to 1in favor of exzguum. Thewriter has always 
found the two species associated together (in Illinois). In 
view of this fact it may be possible that one is a variety of the 
other, instead of a distinct species, as the two forms may inter- 
breed. This, however, is a subject for future study. Like 
exiguum the present species is widely distributed. 
The genus Carychium is of great interest to the student of 
evolution, as it is more than probable that the Mollusca be- 
came terrestrial air-breathers through a form similar to Cary- 
chium, Alexia or Melampus. They are almost, but not quite, 
amphibious. Cavychium is almost as frequently found in water 
as out of it, that is, under logs and stones in such moist locali- 
ties that the animal is immersed in water. It has never been 
found, so far as known to the writer, in ponds or creeks, as is 
Limnea. 
Superfamily Hygrophila.* 
“Teguments smooth; living in fresh water and only com- 
ing to the surface occasionally to renew their supply of air. 
Tentacles contractile, with eyes at their base. Jaw simple in 
Physa and compound in Limng@a and Planorbis, composed of 
three pieces corresponding to the three lips of the mouth, and 
not completely separated (Fig. 81). Central and lateral teeth 
as in Helicide, marginals pectinate or serriform.” 
“Male orifice near the tentacle, female at the base of the 
neck, near the respiratory opening. Eggs contained together 
in a gelatinous, transparent capsule. Phytophagous (Physa is 
sometimes carnivorous). Swimming ina reversed position at 
the surface of the water.’’T 
_ *The writer is greatly indebted to Mr. Bryant Walker, of Detroit, Mich., for much as- 
sistance in preparing the account of the fresh water Pulmonates. 
Tryon, Struct. and Syst. Conch., Vol. III, p. 99. 
