
MOLLUSCS, VERMES AND HYDROZOA 

P. heterostropha, Fig. 176, reaches a length of shell 34 inch and is to 
be found on the water plants of ponds and streams quite generally in the 
Eastern and Middle States. The elongated translucent polished spindle- 
shaped shell is ovate, of ; 
yellowish-brown color 
terminating rather 
abruptly in an acute apex, 
and the large aperture 1s 
oval, about three-fourths 
the length of the shell. 
Of the four or five slight- FIG. 176. Physa heterostropha, Enlarged. 
ly convex whorls the body whorl is inflated and more than half the length 
of the shell. The suture is well marked, the apex pointed and the aperture 
narrow and longer than the spire. The body is yellowish-grey or darker, 
dotted with whitish-yellow; and the long and slender tentacles are pointed. 
It is an active snail but of objectionable vegetable feeding habit. It de- 
posits 6 to 20 eggs in a capsule, which hatch in 15 to 20 days. Found 
generally throughout the Eastern and Middle States and in the Delaware 
and Schuylkill rivers. It is frequently introduced into the aquarium with 
aquatic plants, and is one of the most common freshwater snails. 
Aplexa hypnorum, Fig. 177, has a slender translucent highly polished 
yellowish-brown or ochre shell, of five or six oblique revolving flattened 

whorls with convex apex 
and narrow aperture. The 
body is black, which tends 
to give the thin shell also a 
black color. It inhabits 
stagnant pools and is found 
FIG. 177. Aplexa hypnorum. Enlarged. in slow-flowing streams of 
Vermont, Massachusetts, New York, Pennsylvaniaand the Western States. 
There are many other species of Physa and Aplexa, but not native 
to the Easten and Middle States. As they are largely herbivorous and 
therefore objectionable in the aquarium they need not be described. 
GeneraL Remarks. Descriptions of the colors of the shells of 
snails can only be done approximately as they are variable and depend 
upon the character of the water which the snails inhabit. The presence of 

iron, for instance, stain them to darker colors or black, while slight acid- 
ities bleach them to paler colors. If the empty shells are laid in oxalic 
acid their true colors will soon appear. ‘Those given are based on the ob- 
servations of the author, either of living snails in his aquaria or of those 
in his cabinet collection. 
Sif 
