NIAGARA GROUP. 
287 
649. 2. PLATYOSTOMA NIAGARENSIS (n. sp.). 
Pl. LX. Fig. 1 a-v. 
Compare N&rita haliotis, Sow. in Murchison., Sil. System, pag. 625, pl. 12, fig. 16. 
Globose ; volutions three or four ; body-whorl large, inflated towards the aperture which is 
dilated; sutures deep; spire depressed (rarely elevated) ; shell thin; surface striated across 
the volutions, and in well preserved specimens longitudinally marked by filiform undulating 
striae. 
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 un¬ 
dulating longitudinal striae do not always appear, and sometimes only upon a portion of the 
surface, even when there is no appearance of abrasion. In other examples they have evidently 
been worn off, leaving the transverse striae well preserved. 
Fig. 1 a, b, c . Young individuals, where the spire is depressed as low as the outer volution. 
These specimens show only transverse striae. 
Fig. 1 d. An individual having the spire equally depressed, and the surface conspicuously marked 
by longitudinal striae. 
Fig. 1 e. Profile view, showing the depressed spire. 
Fig. 1 /. A small specimen having an elevated spire, with the surface marked as in fig. 1 d. 
Fig. 1 g. View looking on the spire of a similar specimen. 
Fig. 1 h. A small specimen having the spire much elevated, and the volutions longitudinally 
and transversely striated. 
Fig. 1 i, k, l. Back, summit and front views of a globose specimen preserving its natural pro¬ 
portions. The spire is moderately elevated, the volutions very rotund, and the aperture 
tolerably well preserved. The surface is strongly marked by transverse striae and 
faint indications of longitudinal ones. On the middle of the last whorl there is an 
elevated band reaching half way to the aperture, beyond which the surface is plainly 
v striated. 
Fig. 1 m, n. Two views of a similar specimen, having the aperture somewhat more expanded. 
Fig. 1 o, p. Two views of a larger individual with an expanded aperture and a strong fold upon 
the back of the volution, and a sinus in the margin of the aperture. 
Fig. 1 r. A similar larger specimen. 
Fig. 1 5, t. View of spire, and partial front view of a large specimen from which the shell is 
partially exfoliated. In this one there is no evidence of a band on the middle of the 
volution, and but a slight arching backwards of the striae. 
Fig. 1 u, v. View of the summit of two other individuals having the usual depressed spire of 
this species. 
Position and localities. This species occurs at Lockport, Rochester, Wolcott, and other 
places where the shale is exposed. It is never abundant, though occurring in nearly all localities. 
