LOWER HELDERBERG ROCKS. 
399 
Murcliisonia Mlirata ( n. s.). 
Plate LY. Fig. 2. 
The specimen is a fragment preserving two volutions, the margins of which are 
marked by a fine elevated line on each side of the central spiral band, and parallel 
with it. The surface is finely striated. 
Geological position and locality. In the shaly limestone of the Lower Helderberg 
group : Albany county. 
Platyostoma. 
The Platyostomae of Conrad are globose shells with low spires, having 
columella : the last volution is extremely expanded, the aperture very 
large, and the columellar lip thickened. 
The following is the description of the Genus Platyostoma, as given 
by Mr. Conrad in the Journal of the Academy of Natural Sciences, Vol. 
viii, p. 275 : 
« PLATYOSTOMA, Conrad. 
u Shell subglobose : spire short; aperture very large, suborbicular, dilated; labrum 
“ joining the body whorl at right angles to the axis of the shell.” 
These shells are often distorted by pressure to a great extent, and it 
is not possible always to distinguish the casts of this genus from those of 
the Strophostylus, or from those of some species of the Platyceras of 
Conrad. 
The P. ventricosa is given as the type of the 
genus, and the accompanying figure is copied 
from the outline of the shell as given by Mr. 
Conrad on Plate xvii of the volume cited. 
Platyostoma. 
