Geology of Upper Iilinois. 153 
were recognized Encrinal stems, a large Spirifer, the Pholadomya 
elongata, (of Morron,) and a species of Producta, of which 
a figure is annexed, and which I shall denominate the semi- 
Fig. 9. 
netata. Description.—Length rather surpassing the breadth : 
slightly inequilateral. Concave valve with a fold in the middle. 
Lower valve slightly concave. Hinge-line two thirds the length. 
Vout. XXXIV.—No, 1. 20 
