118 



LAND AND FRESH-WATER SHELLS OF N. A. [PART II. 



planorbula. 



I Bulla fiuviatilis, Say.— Shell suboval, pellucid, pale yellowish-white 

 finely wrinkled ; volutions three ; body whirl large, with a prominently 

 carinated shoulder bounding the spire ; spire perfectly flat or slightly con- 

 cave, giving to the shell a perfectly truncated appearance in that part ; 

 aperture longer than the columella, oblong-ovate, extending beyond the 

 tip of the spire ; umbilicus profound, edged by a slight carina. Length, 

 of the aperture one-fifth of an inch ; greatest breadth somewhat less. 



Inhabits the river Delaware. This species seems to be rather rare ; it 

 was discovered by Mr. Aaron Stone, deeply imbedded in the mud. Mr. 

 William Hyde, of this city, has since found specimens of it amongst some 

 dead shells of other genera assembled in a small inlet of the river. {Say.) 



Physa planorbula, DeKat. — Shell small, thin and fragile, sinistral, cylin- 

 drical above, tapering beneath, abruptly truncated on the summit ; apex 

 very slightly elevated above the truncation. Whirls four, the surface 

 smooth, with minute revolving lines crossed by others 

 p- -^nrj equally minute. Body whirl with an acute shoulder, the 

 edge being slightly turned over. Aperture as long as the 

 shell, narrow above, dilated beneath, and broadly rounded. 

 Outer lip acute, thin and reflected over the enlarged um- 

 bilicus. Color light amber. Length 0.2 inch. 



This singular shell was found by Mr. G. B. Clendining at 

 the Cohoes Falls, adhering to stones. I have adopted the 

 name proposed by iis. discoverer. It was alive, and was 

 destitute of an opercule. It is supposed by some conchologists to be a young 

 Planorbis, but I cannot learn that it has been found in the intermediate 

 stages. It is placed provisionally here ; but if a perfect animal, must 

 constitute a new genus. I am inclined to suspect that it is the animal 

 described by Say as Bulla fluviatUis. {DeKay.) 



Planorhis merjastoma, DeK\y. — Shell large, coarse and solid. Whirls 

 nearly five, rounded, with coarse transverse waving wrinkles, becoming 

 larger towards the mouth. A large prominence on 

 Fig. 198. the body whirl nearly opposite to the aperture, pro- 



ducing an obtuse angle. Spire depressed, with the 

 suture distinct ; beneath, the volutions are exhibited 

 nearly to the apex. Mouth dilated, but somewhat 

 contracted at the margin, 0.3 inch wide and 0.4 high ; 

 its lower portion rounded, arising from the lower part 

 PlanorhhrMijn stoma. of the penultimate whirl; line of the upper margin 

 more nearly straight. In the young, the aperture is 

 not so much dilated, and is obscurely trigonal, with the lower margin be- 

 neath the plane of the transvei-se diameter of the shell. Color olivaceous, 

 tinged with yellowish within the aperture. In the young, black, with the 

 interior of the aperture dull reddish. Diameter 0.8, height 0.3 inch. 



This Planorbis was found near Lak.? Ontario, and appears to be different 

 from any species yet described. In its aperture it resembles the small P. 

 dUatatus of Gould, but is otherwise very distinct. {DcKay.) 



