The River Snails 



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

 Two faint bands traverse each whorl. Length, 2J 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, |- 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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