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New Fresh- Water Shells. 327 
scarcely falling below it; last whorl much larger 
than the spire, flattened above, then abruptly curving 
downwards, (in the young shell, at the upper third of 
the last whorl, is a carina, which is gradually modi- 
fied into the abrupt curvature, in the progress of 
growth, ) subcarinate below, as are also the preceding 
whorls ; aperture nearly orbicular, interrupted by the 
last whorl in about one-fifth of its circumference, ad- 
vancing above ; wmbilicus as broad as the last whorl, 
rather deep, exhibiting all the volutions. 
Height (of the last whorl), .09 inch; greatest 
breadth, .23 inch; least breadth, .18 inch.  . 
Cabinets of the Bost. Soc. Nat. Hist. ; of Middle- 
bury College ; of Mr. Shiverick; and my own. 
Habitat. New Bedford. jr 
Remarks. For this species I am indebted to Mr. 
Shiverick. It differs from P. parvus, Say, in being 
much less broadly and more deeply umbilicate be- 
neath; it is also higher. P. parvus, also, in- 
stead of being subcarinate on the lower side of the 
whorls, is much flattened. P. concavus, Anthony, 
MSS., resembles this species, but is more regularly 
convex above and concave beneath. 
PLANORBIS ELEVATUS. 
- Plate Ill. Fig. 16. 
P. testà. parvà, pallid, suprà elevatà, infra alté umbilicaté ; an- 
fractibus quatuor; suturà valdé impressà; apertura subrotundata ; 
labro supra prominente. 
Shell horn color, finely striate ; whorls four, as 
high as wide; last whorl well rounded, very indis- 
tinctly carinate below ; inclination to the left about 
