LOWER HELDERBERG ROCKS. 



39» 



Murcliisonia bilirata ( n. &.). 



Plate LV. Fio. 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. 



PL.4TY0ST0MA. 



The Platyostomse 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. Conead in the Journal of the Academy of Natural Sciences, Vol. 



viii, p. 275 : 



« PLATTOSTOMA, Conrad. 



" Shell siil^lobose : 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 PtATrcERAS 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. 



Plattobtoha. 



