46 The Fauxa of the Iveyser Member of the 



outer volution : volutions about three, the first and second very minute, 

 and the last one rapidly expanding; aperture campanulate, with the lip 

 broadly reflexed on the posterior and part of the right side. Surface 

 marked by fine thread-like striae, which often become lamellose on the last 

 volution, and these are cancellated by very fine revolving stria." Hall, 

 1859. 



Occurrence. — Heldekbeeg Formation", Keyser ? Member. Cash 

 Valley. 



Collection. — U. S. National Museum. 



Genus PLATYOSTOMA Conrad 



Platyostoma niagarense Hall 

 Plate LXXXVII, Figs. 3, 4 

 Platyostoma niagarense Hall, 1852, Pal. N. Y., vol. 11, p. 287, pi. Ix, figs. la-v. 



Description. — " Globose ; volutions three or four ; body whorl large, in- 

 flated towards the aperture which is dilated ; sutures deep ; spire depressed 

 (rarely elevated) ; shell thin; surface striated across the volutions, and in 

 Avell-preserved specimens longitudinally marked by filiform undulating 

 stria. The spire appears to be depressed often when the shell retains its 

 natural proportions, and at other times from pressure ; in a few examples 

 it is considerably elevated. The fine undulating longitudinal striaj do not 

 always appear, and sometimes only upon a ^^ortion of the surface, even 

 when there is no appearance of abrasion. In other examples they have 

 evidently been worn off, leaving the transverse strige well preserved." 

 Hall, 1852. 



Length 1.8 cm.; diameter 1.9 cm. 



Occurrence. — Helderberg Fokmatiox, Keyser Member. Viaduct 

 Cumberland. 



Collection. — U. S. National Museum. 



