PLANORBIS. 



119 



Planorhis macroxtomus. — Shell in many points closely resembling Pi. 

 lentus, Say, of which perhaps it may only be 

 a variety. It is much larger, higher, and has ^'S- I''''- 



deeper costcE ; its lines of growth are veiy 

 prominently marked ; the upper angle of the 

 whirls, as sliown in the mouth, is more promi- 

 nent. LijJ widely expanded, and reflected, 

 covered with a white enamel. In this latter 

 character it differs from all the American 

 species of PlatiorJiis. It is a species neai'ly 

 allied to Planofbis lentus and P. tricolvis ; but 

 ajjparently distinct from both. (^Whittaves.) 



I am inclined to believe PJ. proboti- 

 cideuH to be identical witli PI. trivolvis. 

 The figure of Potiez & Micliaud, copied 

 below, represents a more flattened shell 

 than usually found in trivolvis, and the 

 ■whirls are more numerous. The original 

 description also is given below. 



Planorhis prohoscideus (Mke., teste Ziegler). 

 — This shell has a slight resemblance in form 

 to a young PL corneus, but it has strong longi- 

 tudinal strise ; the six whirls are carinated 

 towards the two umbilici, and rounded at the 

 periphery ; the upper umbilicus is deep, as well as 

 the lower, which is also large ; the aperture is sub- 

 trigonal and irregular, which is caused by a depression 

 below. Diam. 20 mill., height 10 mill. 



North America in Ohio. (^Poliez ^- Michaud.) 



Planorbis macrostornus. 



Fig. 200. 



A copy of Prof. Haldeman's description and 

 figure of PI. trivolvis, var. fallax, now follow. 



Planorhis trii-olvis, v&v. fallax. — ^4ni'mrt?darkbrowni 

 minutely dotted with ochre-yellow, upon the parts 

 which are usually exposed ; tentacles very long, 

 colored like the body, except that the tint is some- 

 what lighter near the base ; foot posterior to the 

 neck, about equal in length to the head in front of tlie 

 tentacles. 



Shell thin in texture, translucent, and transversely 

 striate ; two and a half turns are visible above, the 

 remaining ones disajapearing in the narrow umbilic ; 

 lower side carinated, having a wide, shallow cup, as 



PlanorMs 

 prohoscidbus. 



