22 nil-; nautilus. 



antly in ponds and streams of greater or lesser size, adhering to sticks 



or stones, and crawling over the muddy bottom. Inhabits either 

 running water or stagnant pools. 



Remarks : This is a very common and handsome species. Its 

 habits are active, moving with a rapid, steady, gliding motion. It is 

 very interesting to watch a number of Physa- in an aquarium ; as 

 they are crawling along tlie bottom, one will be seen to rise suddenly 

 to the top of the water and move along with the foot applied to the 

 surface, the shell hanging down. Again, they may be seen descend- 

 ing, suspended by a thin thread of mucus. When the animal rises 

 suddenly, the branchial cavity opens with a faint clicking sound, 

 probably due to the pressure of air in the lung. This species fre- 

 quently inhabits water as cold as the freezing point, and may be ob- 

 served in winter gliding along the bottom of a pond when the surface 

 is frozen. The eggs are deposited on stones, the under side of sticks, 

 etc.. and are composed of large, glairy, transparent masses. 



Several Physae kept in captivity laid four egg masses on April 23, 

 1897. The egg masses measured 20 by 4 mill., and contained from 

 120 to 200 eggs. On April 24, ten additional egg masses were laid. 

 The jar contained 15 individuals. On June 3, in the afternoon, the 

 writer noticed a number of young in a jar containing egg masses 

 deposited probably in the latter part of April. The young were half 

 a mill, in length, vitreous in appearance and perfectly transparent. 

 They were very lively, crawling about the jar and feeding voraciously 

 upon the scum found on the sides of the glass. The heart pulsated 

 120 times per minute. On June loth the young had increased to 

 one mill, in length. About a week later, unfortunately, the whole lot 

 died, so that no further notes could be taken. 



Physa gyrina is by far the most common species of the genus (I 

 might say of any germs) found in the area, and has been found in all 

 parts of northern Illinois. It was at first confused with keterosd-opha, 

 but that species has a smooth shell (see above) and is not found in any 

 numbers in the area ; it is very probable that heterostropha is not 

 found west of the Mississippi River, and the quotations of this 

 species from western localities were probably founded on gyrina, 

 sayii, gabbi, Integra, etc. This species is very variable in this 

 region, some forms approaching ampullacea Gould, while others 

 might be taken for gabbi Tryon, or virginea Gould, so far as form 

 goes. It is probable that some west coast names will be added to 

 the above synonymy, when more study is given to this genus. 



