308 THE CHICAGO ACADEMY OF SCIENCES. 



The writer has attempted to revise the species found in 

 Northern Illinois, and the late Mr. O. A. Crandall, of Sedalia, 

 Mo., has published some very valuable notes on the American 

 Physae in The Nautilus for 1901. This gentleman believed that 

 the most reliable characteristics for determination were tex- 

 ture, structure and sculpture. He also considered that the 

 length of time required for a species to reach maturity might 

 also serve as a character of importance. He found, as have 

 other students of this family, that some species attain their full 

 growth in one year while others require two or three. He 

 therefore proposed the terms annuan, biannuan and triannuan 

 for the species which reach maturity in one, two and three 

 years. As a whole,-the writer agrees with the conclusions of 

 Mr. Crandall. 



FIG. 107. 

 Animal of PHYSA. (Binney, Fig. 123.) 



Distribution: North America, Europe, East Indies. 



KEY TO SPECIES OF PHYSA. 



A. Shell smooth, broad, spire short. Annuan heterostropha 



B. Shell with impressed spiral lines. 



a. Shell rather broad, ovate, spire short, acute; aperture 

 wide and spreading; whorls four and one-half to five; 

 shell thinner than b; peristome callus bordered by red. 

 Annuan sayii 



b. Shell elongated or cylindrical, narrow, spire generally 

 long; aperture very narrow; whorls five to six; peri- 

 stome callus bordered by red. Triannuan gyrina 



c. Shell broad, inclining to be shouldered; spire sharply 

 conic; aperture roundly oval; peristome callus white, 

 without red border. Biannuan Integra 



125. Physa heterostropha Say,* pi. xxxiv, fig. 2. 



Limncea heterostropha SAY, Nich. Encycl., Amer. ed., pi. i, fig. 6, 1817. 

 Physa fontana HALDEMAN, Mon., pt. 2, p. 3 of cover; Physa p 26 



1841. 

 Physa heterostropha alba CRANDALL, The Nautilus, Vol. XV, p. 29, 



1901. 



Shell: Polished, subovate, whorls four to four and one- 

 half; spire moderately elevated, acute, the whorls slightly con- 



*The greater part of the subject-matter on Physa was published in The Nautilus, Vol. 

 XIV, pp. 16-24. 1900- 



