256 THE CHICAGO ACADEMY OF SCIENCES. 



are five and one-half whorls; the aperture \sjust 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: Jaw 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 exiguum, the ratio 

 being about 3 to I in favor of exiguum. The writer 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. Carychium 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 

 Limncsa. 



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 Limncea 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 Helicidae, 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 in a reversed position at 

 the surface of the water."f 



VThe writer is greatly indebted to Mr. Bryant Walker, of Detroit, Mich., for much as- 

 sistance in preparing the account of the fresh water Pulmonates. 

 tTryon, Struct, and Syst. Conch., Vol. Ill, p. 99. 



