295. Upper whorls ribbed; about ^/^"\ south-central states (Ind. to Ala.) 



Gastrod-onia interna (Say) 

 Whorls with growth lines only; about Y^"', Penna. to Ala. 

 Ventridens gularis (Say) 



296. Spire rather low; east of the Mississippi 



"Ventridens demissus (Binney) 

 Spire more elevated (height almost three-fourths width) ; westward to 

 Okla. 



Ventridens ligera (Say) 



297. Umbilicus absent or extremely minute; about Vs"; northwestern 



states 298, 



With a small umbilicus; with lamellae or radial rows of teeth within 

 base of last whorl and usually visible through the shell, in young speci' 

 mens, sometimes persisting in the adult; about Vs" to %"; eastern and 

 central states to Texas 299. 



298. Spire somewhat elevated; with radial grooves in shell 



Pristiloma stearnsi (Bland) 

 Spire depressed; shell almost smooth 

 Pristiloma subrupicola (Dall) 



299. With eight whorls 



Paravitrea andrewsae (Binney) 

 With five or six whorls 300. 



300. Body whorl irregularly striate or grooved 301. 

 Body whorl with close, evenly spaced striae or grooves 302. 



301. Young often with pairs of teeth within; from western 111. and Tenn. to 



Okla. 



Paravitrea significans (Bland) 

 Often without teeth in both young and adult; from eastern 111. and 

 Tenn. to N. C. 



Paravitrea capsella (Gould) 



302. With radial rows of teeth within base of body whorl and often visible 



through the shell; Maine to Ala. and Arkansas 



Paravitrea midtidentata (Binney) Toothed Leaf Snail 

 Without teeth; often with one or more lamellae within base of body 

 whorl; Tenn. to N. C. 303. 



303. Body whorl with minute spiral lines; with or without internal lamellae 



Paravitrea wal\eri (Pilsbry) 

 Body whorl without spiral lines; usually with internal lamellae 

 Paravitrea lamellidens (Pilsbry) 



KEY TO THE PRINCIPAL GENERA AND SPECIES OF CLAMS 

 AND CLAM-LIKE MOLLUSKS 



1. Shell without nacre (mother-of-pearl) except around the edges, out' 

 side of the pallial line; cardinal teeth situated under the beaks, with 

 the lateral teeth both before and behind; shell seldom reaching one 

 inch in length; generally distributed Finger-nail Shells 2. 



146 



