328 NEW YORK STATE MUSEUM 



side by a distinct fold which reaches part way across the body whorl and 



gives a squared outline to the early part of the same whorl. This specimen 



however shows but very obscure traces of revolving striae, which are given 



as a characteristic feature of the species. Phragmostoma triliratum 



is cited from the Chemung fauna of Steuben county, N. Y. 



Habitat. Genesee province ; Naples subprovince. Hamilton gully 



Honeoye lake. 



Phragmostoma chautauquae sp. nov. 



Plate 17, fig. 1-11 



cf. Bellerophon striatus (Phil.) Hall, Geology of New York; rep't on fourth 

 dist. 1843. p. 246, fig. 107, 7 



Shell somewhat larger than other species of the genus, with narrow 

 spire rapidly widening to medium broad body and thenceforward abruptly 

 expanding to the aperture, which is scarcely explanate. Dorsum angular, 

 sides sloping thence rather abruptly with a slightly concave surface. Slit 

 band very narrow, often obliterated by slight lateral compression, which 

 changes it to a median keel. The emargination of the anterior edge pro- 

 duced by the slit band is quite deep. The inner lip of the peristome is 

 reflected over the ultimate whorl, and a projecting flattened callus is formed 

 on this surface, not extending however as far into the inner cavity as in the 

 species P. natator and P. incisum. Surface of the adult with only 

 fine regular and crowded concentric growth lines. 



Young conditions, however, display a quite different style of ornamen- 

 tation. The early whorls are covered with fine revolving elevated striae, 

 which are closely set and traverse the entire surface, covering to obliteration 

 the place of the slit band. These fine lines, with later growth, become 

 interrupted and broken up into series of more or less completely discon- 

 nected tubercles, which at times press together from adjoining rows. 

 Eventually the arrangement of these tubercles is made more distinct by the 

 appearance of concentric lines, and in this stage the former clearly appear 

 as the result of cancelation of the surface. Meanwhile, with the introduc- 

 tion of the concentric lines, the slit band has come into prominence, the 

 concentric lines looping backward on its surface. Gradually the traces of 



