No. 109,J 



79 



on the middle of the dorsal valve, so as to form an extremely 

 obscure mesial fold, and two or tliree as much depressed on 

 the ventral valve : plications on the front marked with a 

 longitudinal depressed line, and remains of much liner closely 

 arranged zigzag lines of growth. 



. This species belongs to the type of R. wilsoni, and is one of those forms 

 which are often referred to that species. In some of its varieties it resem- 

 bles R. pyramidata, but is more angular on the sides, and never so ab- 

 ruptly sloping to the beaks. In some of its phases it more nearly resembles 

 the R. nucleolata in form, but the plications arc stronger. 



Among many hundreds of individuals of the preceding species collected 

 from the Shaly limestone, I have not seen one of this species, and it ap- 

 pears to be restricted to a bed in the upper part of the group. 



Geological 'position and locality. Upper Pentamerus limestone of the 

 Lower Helderberg group, Schoharie and Carlisle. 



Rhynchonella venteicosa. 



Rhynchonella CAIUPBELLANA. 



Pal. N.Y. Vol. iii, pi. 43, f. 2. 



Shell longitudinally oval, ovate or oblong, laterally compressed, 

 two-thirds as broad as long, length and height about equal : 

 dorsal valve the larger, elevated near the front into a broad 



