THE OTTAWA NATURALIST 



Vol. XXX. DECEMBER, 1916. No. 9. 



COMAROCYSTITES AND CARYOCRINITES. 



Cysttds with Pinnulieerous Free Arms. 



By A. F. Foerste, Dayton, Ohio. 



(Continued from page 93.) 



Detailed Description of Comarocystites shumardi, 

 Meek and Worthen. 



21. Comarocystites shumardi, (Figures 1A, B, C, on plate IV) 

 differs from Comarocystites punctatus chiefly in the more deeply and 

 more angularly concave thecal plates. These features are well shown 

 by the type specimen illustrated by figures 1A, and IB on plate I in 

 volume III of the Geological Survey of Illinois. In plates eight to 

 ten millimeters in width the depth of the concavity usually is about 

 three millimeters, in one case equalling four millimeters. From the 

 center of the concavity the inversely pyramidal flattened walls of the 

 concavity slope upward and outward; along lines leading from the 

 center to the angles of these concavities, the flattened walls are separ- 

 ated by more or less distinct narrow grooves, giving the exterior surface 

 of each thecal plate a stellately indented appearance (Fig. 1C). The 

 number of thecal plates in the type specimen probably was somewhere 

 between 65 and 70. The general shape of the theca is shorter and 

 more globose-obovate than in Comarocystites punctatus. The line of 

 demarcation between the basal plates is indistinctly defined, but these 

 plates probably numbered more than three. 



In his original description of Comarocystites punctatus (Can- 

 adian Journal, 2, 1854, p. 268) Billings stated that "upon the upper 

 joint of the column stand three low but broad pentagonal plates, with 

 serrated edges above. These form a narrow circular pelvis, and are so 

 closely united at their sides that it is difficult to detect the lines of 

 division between them." It probably was the attempt to make their 



