PLEUROCERA. 137 



larger have been in my possession for a long time. They are from 

 Dr. Troost, and are more inflated. While the older part is dark 

 brown, the newer part is dark green, and the interior partakes of 

 these colors. The specimen from Mr. SaflTord is rather smaller and 

 browner, is purplish within and is thickened on the outer lip near the 

 base. All have a light line under the suture. That from Dr. Currey 

 is about half grown, and has two broad bands. The largest specimen 

 is figured, the lower part of the specimen is more expanded than the 

 others, and is very remarkable in this respect. In outline it is allied 

 to M. pinguis (nobis), but differs much in the form of the aperture. 

 The aperture is nearly half the length of the shell.— Z-ea. ■ 



82. P. trocliulus. Lea. 



Trypnnostoma trochulus, Lea, Proc. Acad. Nat. Sci., p. 175, 1862. Jour. Acad. 

 Nat. Sci., V, pt. 3, p. 283, t. 37, f. 103. Oba. ix, p. 104. 



Description. — Shell smooth, top-shaped, very much swollen, yellow, 

 single banded below; spire very obtuse; sutures impressed; whorls 

 six, flattened above and inflated below ; aperture large, rhomboidal, 

 whitish and single-banded within ; outer lip acute, sinuous ; 



" . i' . , Fig. 255. 



columella thickened below and very much twisted. 



Habitat. — Holston River, Tennessee; Prof. G. Troost. 



Diameter, -37 ; length, '49 inch. 



Observations. — A single specimen of this pretty little spe- 

 cies was received from Prof. Troost, a long time since, with Melania 

 turgida (nobis), but it is a very different species, having a more char- 

 acteristic auger-shaped mouth, and tliis specimen has a single band, 

 while four specimens of turgida have each five bands. It is also 

 top-shaped while the turgida is globose. It is not easily confounded 

 with any other species, being wider for its length than any other 

 Trypanostoma with which I am acquainted. The aperture is full one- 

 half the length of the shell, and the body-whorl is nearly two-thirds 

 the length of the whole shell. — Lea. 



83. P. napoideum, Lea. 



Trypanostoma napoideum. Lea, Proc. Acad. Nat. Sci., p. 112, 1801. Jour. Acad. 

 Nat. Sci., vi, p. US, t. 23, f. 54, 18G7. 



Description. — Shell smooth, obtusely conical, rather thick, horn- 

 color, witliout bands; .spire short, pointed at the apex; sutures 



