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 

 and end of tentacles; mantle margin simple, not reflected over 

 the shell. Genital orifice on left side. 



yaw: 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 





FIG. 113. 



Radula of APLEXA HYPNORUM Linne. (Original.) c, cusp of central 

 tooth; L, lateral teeth. 



teeth (39-1-39) in a single row and counted 230 rows in a 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 maybe 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- 



