88 



LAND AND FRESH-WATER SHELLS OF N. A. 



PART IIL 



the sinuous peritreme, the revolving strisB, the short spire, the 

 lieavy callus upon the parietal wall of the aperture. Some of 

 them are figured in I^ig. 72 to 75. 



I give below the original description of Mr. Say, and a foc- 

 siniile of one of his figures (Fig. tlSj. The shell figured as Pal. 

 decisa in the American Conchology may, perhaps, be a form of 

 31. ponderosa. (See Fig. 84.) 



Fig. 76. 



Paludina ponderosa. 



Paludina ponderosa, Say. — Shell somewhat ventricose, much thickened, 

 olivaceous or blackish ; spire not much elongated, much shorter than the 

 aperture, eroded at tip, but not truncated; 

 whirls five, slightly wrinkled across ; suture 

 profoundly impressed ; aperture subovate, more 

 than half the length of the shell ; labium with 

 much calcareous deposit, and thickened into a 

 callosity at the superior angle; within tinged 

 with blue. 



Inhabits Ohio River. 



Greatest length, one inch and 11-20. Trans- 

 verse diameter one inch and 1-10. 



This shell is common at the falls of the 

 Ohio, and is a very remarkably thick and 

 ponderous species. It bears a striking resem- 

 blance to P. decisa, and has, without doubt, 

 been generally considered as the same ; but 

 it differs from that species in being much more 

 incrassated and heavy ; and although much 

 decorticated and eroded upon the spire, the tip is not truncated. In the 

 labrum also is a distinctive character ; by comparison this part will be 

 perceived to be less arcuated in its superior limb than the corresponding 

 part in decisa. 



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

 In its full grown state it is very thick and ponderous, enlarging so much 

 in its body whirl, as to appear very different from the young shell. In 

 the early stages of growth it resembles P. decisa, Nobis, from which indeed 

 the back view would hardly distinguish it; but a sufficiently distinctive 

 character resides in the lower part of the labium, which in the decisa is 

 not obviously produced, whereas in the present species it is considerably 

 advanced, as in many species of Melania, to which genus it is closely 

 allied. (Snij.) 



I have no donbt that a young specimen of 3TeJanth,o ponderosa 

 is the type of Paludina regularis, Lea. My figure is drawn 

 from a specimen determined by him, and now deposited in the 

 collection of the Smithsonian Institution (Xo. 9016). The spire 



