DESCRIPTION. 



Shell somewhat ventricose, much thickened, greenish 

 or olivaceous : ^ire prominent : ivhorls six, slightly wrin- 

 kled across : suture deeply indented : aperture ovate, above 

 narrowed a little, but obtuse at the superior extremity : la- 

 bium with much calcareous deposit, often thickened into 

 a callosity at the superior angle : labrum very obviously 

 more prominent towards the base : within bluish- white. 



OBSERVATIONS. 



This shell is common in many parts of the Ohio as well 

 as of its tributaries. In its full grown state it is very thick 

 and ponderous, enlarging so much in its body whorl, as to 

 appear very different from the young shell. In the early 

 stages of growth it resembles P. decisa^ Nob. from which 

 indeed the back view would hardly distinguish it ; but a 

 sufficiently distinctive character resides in the lower part 

 of the labrum, which in the decisa is not obviously produ- 

 ced, whereas in the present species it is considerably ad- 

 vanced as in many species of Melania, to which genus it 

 is closely related. 



REFERENCE TO THE PLATE. 



Figure 1st represents a large and very perfect specimen. 

 PLATE XXX. 



