21 



nati on the Ohio, and at Engineer Cantonment at Council Bluff, 

 on the Missouri. 



Besides the above species, I have observed in the western 

 regions the following known species, which I described in the 

 American edition of Nicholson's Encyclopasdia, and in the Journal 

 of the Academy. 



H. ALBOLABRis. — Conmiou as far as Council Bluff. 



11. TiiYROiDUS. — On the banks of the Ohio, Mississippi and 

 Missouri. The animal is of a pale whitish or yellowisli color, 

 immaculate. 



H. ALTERNATA. — On the banks of the Ohio, Mississippi and 

 Missouri Kivers ; this species varies in being somewhat larger, and 

 in having a rather more elevated spire. The animal is of a dirty 

 yellowish orange color. The foot obtusely terminated behind, 

 head and tentacula pale bluish, eyes blackish. Shell nine-tenths 

 of an inch in breadth. 



H. HiRsrTA. — Common as far as Council Bluff. 



H. LABYRINTHICA. " " " 



H. MINUTA. " " *' 



H. PERSPECTIVA. — Occasionally occurs on the banks of the 

 Missouri, and other western streams, and in some parts com- 

 mon. 



PoLYGYRA PLICATA. — Shell convex beneath, depressed above, 

 spire slightly elevated ; whorls five, compressed, crossed by nu- 

 merous raised, equidistant lines, which form grooves between 

 them ; aperture subreniform, labrum reflected, regularly arquated 

 describing two-thirds of a circle ; within two-toothed, teeth not 

 separated by a remarkable sinus ; labrum with a profound dupli- 

 cature, which terminates in an acute angle at the centre of the 

 aperture ; beneath exhibiting only two volutions, of which the 

 external one is slightly grooved near the suture. 



Inhabits Alabama. Breadth one-fourth of an inch. Cabinet of 

 Academy. 



This species is about the same size as P. avara, but, besides 

 other characters, it is sufficiently distinguished by the acute fold 

 of the labrum. It was sent to the Academy by Mr. Samuel 

 Hazard. 



Pupa Arjiifera. — Shell destral ; oblong oval, or somewhat 



