The River Snails 



than /. spinosa, which it imitates in its decoration of stout spines. 

 Two faint bands traverse each whorl. Length, 2^ inches. 



Habitat. — Tennessee. 



I. brevis, Anthony, is stout and short, with stubby spines, 

 five on the keel of each whorl. The canal is broad, but short. 

 Length, 2 inches. Tennessee. 



Genus ANGITREMA, Hald. 



Shell conical, spiny; canal short; aperture angled; columella 

 thickened above and below. About twelve species in Tennessee 

 and neighbouring states. 



The Knotty Angitrema {A. geniculata, Hald.) is stout, 

 solid, almost globular, with a row of round knees on the angled 

 shoulder of the whorls. The flaring aperture is notched at 

 both ends. The double callus on the columella is a noticeable 

 generic trait. Colour, yellowish olive. Length, f inch. 



Habitat. — East Tennessee. 



The Armed Angitrema {A. armigera, Say) is cone-shaped, 

 with flattened and wrinkled whorls, and tubercled on a central 

 keel. This row of knobs is buried by the revolving lip as it 

 grows, though their presence is discoverable just below the 

 sutures. The horny surface is often eroded at the apex; revolving 

 red lines obscurely mark the whorls. Length, i inch. 



Habitat. — Tennessee, Indiana, Kentucky. 



Button's Angitrema (A. Duttoniana, Lea) is a handsome 

 species. The elegant yellow-banded spire is conical, pointed, 

 twice as high as wide. The long aperture is notched above and 

 below. A row of tubercles usually follows the middle of the body 

 whorl. Sometimes there is a keel instead. Length, i inch. 



Habitat. — Tennessee rivers. 



A. verrucosa, Raf., is ellipsoid, with blunt apex and long 

 aperture; the lower whorl only is set with several rows of promi- 

 nent warts. The outer lip is plaited within. Colour, olive brown, 

 with white lining. Length, § inch. Ohio River. 



Sub-Genus LITHASIA, Hald. 



Shell small, oval or short, fusiform, smooth; columella as in 

 Angitrema; no distinct channel. Fourteen species, inhabiting 

 rivers of the Tennessee region. 



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