1894.] NATURAL SCIENCES OF I'H ILADELPHIA. 21 



wall hears an elevated oblique blade which is typically almost 

 straight and never much curved. 



Alt. 8k diara. 16J mm. (No. 64,725). 

 6* " 13 " (No. 64,723). 



The tooth upon the outer li[) is generally bifid. Binney's figures 

 of Triodopsid fallax (Man. Amer. L. Sh., p. 292, fig. 314) represent 

 a form of this subspecies, but not its typical development. That 

 this is not the true H. fallax of Say will be evident to anyone com- 

 paring it with the original description. The characters of the two 

 are best shown in the following table : 



P. fraudulenta. H. fallax, Say's description. 



Spire moderately convex. Spire convex, higher than in tri- 



dent ata. 



Whorls six. Whorls five. 



Parietal tooth straight or nearly Parietal tooth " curving down- 

 so. wards." 



Diameter 11 to 17 mm. Diameter 11] mm. 



Hal)itat : Cumberland Mountain Locality, "vicinity of Philadel- 

 svstem, extending northward i)bia." 



along the mountains to Mary- 

 land and westward throughout 

 the Ohio Valley. 



No shells exhibiting the characters of fraud ale ntn have been found 

 in the cis-Alleghenian region of eastern Pennsylvania or New Jer- 

 sey, so far as I can judge by the collections of Philadelphia coucholo- 

 gists, which cover a great many localities and a long series of years. 

 This region is inhabited by typical tridentnta, its variety jaxtidens, 

 and by the "if. introferens" of Bland and authors generally. 



P. fallax Say. 



Gettysburg, Pa., 64,722. The variations of the tridentata group 

 of Tilodop><is are an extremely intricate study, and strange as it may 

 seem, the names hitherto attached to some of the forms require re- 

 vision. Helix fallax was described by Say from the vicinity of Phila- 

 delphia; but the form heretofore so called is not found near Philadel- 

 phia, nor has it been within the present century, if ever. The 

 Triodopses found in this vicinity are (1) P. trideidafa Say, typical; 

 (2) P. tridoitafi jiixtldens ; and (3) P. introferens Bland. These 

 three forms are represented in the collection of the Academy byspeci- 



