NAPLES FAUNA IN WESTERN NEW YORK, PART 2 329 



the revolving lines disappear, and the concentric striae become closely 

 crowded, till they alone are apparent in final growth stages on the usually 

 exposed surface of the shell. The species presents thus all stages in the 

 variation of ornamentation ; indicates that revolving lines are, in this 

 stock, suggestive of immature conditions and qualifies the value of 

 attempts at generic distinction on the basis of variation in this feature and 

 even in the permanency of the slit band. Umbilication is maintained 

 throughout these early stages, but is lost with the development of mature 

 conditions and the formation of the internal callus. 



Dimensions. The only specimen observed which affords a clue to the 

 outline of the peristome measures 16 mm in width and 22 mm in hight. 

 Usually only the body of the shell is preserved, many of the specimens 

 indicating larger size than this. 



Observations. This species is placed with the genus Phragmostoma on 

 account of its explanate peristome and well developed callus, which is hardly 

 septiform but approaches in development that of the typical species. The 

 exterior markings as usually preserved show marked similarity to those of 

 B. nactus Hall of the Chemung fauna, but the latter, so far as we can 

 judge from the type specimens, hardly appertains to the genus Phragmos- 

 toma, the aperture apparently not being expanded, and the slit band 

 making a very deep emargination of the anterior margin extending for 

 fully one half of the final whorl. 



The original specimen referred toBellerophon striatus Phillips 

 by Hall, as above cited, seems to represent the proximal portion of the final 

 volution in this species and shows the regular concentric striations. 



Habitat. Genesee province; Chautauqua subprovince. Common in 

 the soft shales at Forestville, Smith's Mills, at Correll's point, Lake Erie, 

 near Brocton and at Silver Creek, Chautauqua co., Cattaraugus creek at 

 Versailles, Cattaraugus co. 



