318 THE CHICAGO ACADEMY OF SCIENCES. 
constriction, and auriculated; tentacles long and slender, taper- 
ing to a fine point, eyes placed on bulgings at their inner 
bases; head and neck distinguished from foot by a lateral con- 
striction; color blackish, lighter on base and about the eyes 
andend of tentacles; mantle margin simple, not reflected over 
the shell. Genital orifice on left side. 
Faw: Not examined thoroughly, but apparently as in 
Physa, and cartilaginous, with no accessory plates. 
Radula: With a central tooth as in Physa/(?) excepting 
that it has the cusps differently arranged; teeth on either side 
serrated (comb-like) as in Physa (9-10 serrated), with a very 
long, pedunculated base of attachment, and without interme- 
diate smaller serrations, as in Physa. The writer counted 78 
Fie. 118. 
Radula of APLEXA HYPNORUM Linné. (Original.) c, cusp of central 
tooth; L, lateral teeth. 
teeth (39-1-3g9) in a single row and counted 230 rows ina mem- 
brane which was somewhat broken on the edges. The upper 
part of the pedunculated base has a peculiar lateral attachment 
in the form of a long, narrow projection. This membrane dif- 
fers from Physa principally in lacking the small cusps between 
the longer ones and in the absence of secondary teeth. These 
peculiar lateral attachments may be the secondary teeth, but if 
so they are very long and narrow ( Fig. 113). 
Genitalia: Not observed. Ova deposited without en- 
velope. 
Distribution: North America, Europe, Asia. 
Geological distribution: Pleistocene. 
Habitat: Found in the smaller rivers and lakes on a 
muddy bottom. 
Remarks: A beautiful species, easily known by. its long 
and narrow shell, which is highly polished. It has a strong 
resemblance to some forms of Physa, but may always be dis- 
