ANCYLUS RIVULARIS, Say. 



Plate 1. — Fig. 1. 

 A. testa ovata, sublata, subelevata, apice obtuso. 



SYNONYMS AND REFERENCES. 

 w?. RIVULARIS, Say. Journ. Acad. Nat. Sci., I. 125. 



DESCRIPTION. 



Animal plumbeois, minutely dotted with 

 whitish: a central yellowish longitudinal line 

 upon the head: foot emarginate in front, extend- 

 ing to the mouth, where it is very thin. 



Shell delicate, moderately elevated; sides 

 slightly convex, diverging anteriorly: posterior 

 and dextral slopes concave, anterior slope con- 

 vex, and sinistral one nearly rectilinear: apex 

 subacute, projecting, one-third of the shell 

 posterior to it. 



Color light brown; nacre, in large individuals, 

 white. 



Dimensions. Long. 5, lat. 3.5, elev. 2 milli- 

 metres. 



GEOGRAPmcAL DISTRIBUTION. Thc Delaware 

 and Susquehanna. 



