128 



[No. 4, Long's Expedition, &c. vol. ii. p. 261, et seqq. 1824.] 



Planorbis deplectus. — Shell dextral, depressed; whorls 

 nearly five, minutely and regularly wrinkled across, wider than 

 long, with a much depressed rotundity above, descending to an 

 acute lateral edge below the middle ; spire not impressed j suture 

 indented, but not profoundly; beneath a little concave in the 

 middle, exhibiting one-half of each volution to the apex ; whorls 

 flattened, slightly rounded ; aperture declining very much, sub- 

 oval, the superior portion of the labrum considerably surpas- 

 sing the inferior portion, and taking its origin a little above the 

 carina ; inferior portion of the labrum terminating on the middle 

 of the inferior surface of the penultimate whorl. 



Greatest breadth two-fifths of an inch. 



This shell was presented to me by Dr. Bigsby, who collected 

 many specimens in the waters of the North-west Territory. 



It resembles the cxacuous, nob., but the aperture does not em- 

 brace so large a proportion of the preceding volution, and the 

 ^'olutions on the inferior portions of the shell are consequently 

 more obvious, and the umbilicus is but slightly indented ; the 

 upper portion of the labrum does not extend so far beyond the 

 lower portion, the aperture declines much more, and the carina is 

 less acute. It has also an afl&nity for the carinatus of Europe, 

 but in addition to other differences, the aperture of that species 

 declines but little, if at all, and the carina is an elevated revolv- 

 ing line. The aperture embraces the penultimate volution about 

 as much as in the rotundatus of Europe, to which our shell is also 

 allied, but differs in its declining aperture, and the less degree of 

 rotundity of its whorls on their upper surface. PI. 15, fig. 8.* 



Planorbis corpulentus. — Shell dextral ; whorls more than 

 three, rather rugged with coarse wrinkles, much higher than wide J 

 superior surface much flattened, and edged by an abruplr acute 

 line, which is distinct to the aperture ; sides hardly rounded, and 

 terminating below by another abrupt edge, which is not quite so 

 definite and acute as the superior one ; spire slightly concave ; 

 umbilicus exhibiting a portion of each of the rapidly retiring 

 whorls to the apex ; aperture longer than wide, the superior part 

 extending higher than the preceding volution, and the inferior 



* [Plate 74 of tliia reprint.— -Ed.] 



