150 PHYSA. 
sometimes only one-fourth part of the length 
of the shell; labrum very thin, advanced; la- 
bium tumid, with a thin, loosely adherent 
lamina. 
Animal of a very obscure light green color ; 
whole surface of the body covered with oblong 
dark spots; foot shorter than the shell, lanceo- 
late; tentacles nearly white, rather long, very 
slender; mouth blood-red. Its motions are 
exceedingly rapid; very timid, withdrawing 
itself on the least alarm. 
Length 14, diam. 10 mill. 
Monmouth, Maine. 
No other authenticated locality has been 
discovered, and it has been stated that the 
species is Ph. heterostropha,—the normal 
growth yielding to the influence of water sur- 
charged with saw-dust from a neighboring 
mill. Admitting the influence of the saw-dust 
in causing the loose deposit of the labrum, I 
still incline to consider it a very distinct spe- 
cies. 
(66) 
