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 
Physz 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 Puysa. (Binney, Fig. 123.) 
Distribution: North America, Europe, East Indies. 
KEY TO SPECIES OF PHYSA. 
Shell smooth, broad, spire short. Annuan.............. heterostropha 
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. 
ATINUARE A SE '5 ee fcc RRA ete een eee te ETO TREE oe Sayit 
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.; 05 )65% fone yes cba ae Sahat integra 
o> 
125. Physa heterostropha Say,* pl. xxxiv, fig. 2. 
Limnea heterostropha Say, Nich. Encycl., Amer. ed., pl. 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- 
z *The greater part of the subject-matter on Physa was published in The Nautilus, Vol 
XIV, pp. 16-24, 1900. 
