The River Snails 



The Dilated Lithasia (A. dilatata, Lea) spreads out its 

 white lips below the oval, yellowish green spire, showing the 

 brown lining. Low tubercles are sometimes seen on the shoulder. 

 Length, f inch. 



Habitat. — Tennessee. 



Sub-Genus STREPHOBASIS, Lea 



This small group includes a few conical shells in which the 

 short canal is twisted under the shell. 



A. carta, Hald., is greenish-brown and stoutly cylindrical, 

 with a narrow aperture closed with a dark brown operculum. 

 The canal is drawn under by the twisting of the columella. 

 Length, I inch. 



Habitat. — Tennessee. 



Sub-Genus PLEUROCERA, Raf. 



Shell elongated, conical, regular; aperture with short canal; 

 columella without callus. Tryon describes eighty-two species. 



The Ponderous Pleurocera {A. ponderosa, Say) is a heavy 

 cone of flat coils, the last one keeled. The short lip canal 

 turns to the left. The surface is olive, the lining white. Length, 

 2 inches. 



Habitat. — Tennessee. 



A. undulata, Say, has a handsome elevated spire of broad 

 flat coils that cover a row of knobs, and so produce wavy folds 

 below the deep suture. The white lip projects. Length, ij 

 inches. 



Habitat. — Ohio River. 



A. canaliculata, Say, is distinguished by its distinct 

 groove on the body whorl. Variable in form and size and ranging 

 in colour from pale green or yellow to black, yet it is distinct. 

 It is very common at the falls. Length, i inch. 



Habitat. — Ohio River. 



Genus GONIOBASIS, Lea 



Shell heavy, ovate or elongated; aperture angled in front, 

 but without canal or notch. A large genus of one hundred and 

 fifty species, one-half of the entire family, distributed east of 



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