208 Fresh-Water Shells. 



It is found ill most brooks, ditches, and margins of ponds, 

 wliich are permanent tlirougli the summer, adhering to sticks and 

 stones. 



This shell has a striking resemblance to the P. fontanel of 

 Europe, (Lightfoot, Phil. Trans., Ixxvi. pi. 2, f. 1-4. Montagu, 

 Test. Brit., 462, pi. 6, f 6. PI. nitidus, Mull., Turt., &c.,) except 

 that the aperture is entirely below the sharp edge, instead of 

 embracing nearly an equal portion on each side, as in that shell. 

 It is allied to P. deflecius, Say ; but in that the whorls are more 

 numerous, the exterior edge much rounded, the umbilical region 

 broader and more shallow, and the labrum also embraces bu 

 half of the lower surface of the preceding whorl. Were it among 

 the land shells it would be a most unequivocal Carocolla. 



I cannot but think that the name under which this shell appears 

 in the "Journal of the Academy," is not exactly as was intended 

 by the author, as it is neither a Latin word nor a Latin termina- 

 tion. Supposing that by a typographical error, an o has taken 

 the place of a t, we have a legitimate term, and one very expres- 

 sive of the form of the shell. 



Plakokbis Parvus. — (Say.) 



s\ Shell very small and compressed, discoidal, 

 ^^ light-yellowish horn-color ; right side nearly 

 plane, but excavated at the centre ; left side broadly concave ; 

 Avhorls four, almost equally exhibited on both sides, the outer one 

 usually somewhat angulated at its circumference ; surface 

 minutely marked by the lines of growth, shining, clear ; aperture 

 rounded, rather longer than broad, not inclining to either side, its 

 plane very oblique ; lip sharp, slightly reflected on the left side ; 

 within bluish-white. Greatest diameter I inch, lesser diameter J^ 

 inch, but generally much smaller. 



Animal whitish, dusky above, with a still darker line at tip of 

 tentacula. 



Abundant in brooks and ponds. 



This is the smallest shell of the genus which we have, unless, 

 perhaps, it be P. exa.cuius, which is commouly found of as small 

 a size. It is not difficult to be recognised by its regular figure^ 

 and its very thin, compressed appearance. P. dejlectus, armi- 

 f/ems, examiiis, and hirsutiis, all have marked peculiarities, which 

 at once separate them from this undistinguished species. 



