TJic Fauna of the Maxvillc Limestone. 389 



1909. Cliotliyris hirsnta. Grabau and Shinier, N. A. Index Foss., p. 

 354, fig. 464. . 

 St. Louis and Kaskaskia : Kentucky, Indiana, Illinois, Montana. 



Description. — Shell small, biconvex, sub-circular to obovate 

 in general outline. 



Pedicle valve most convex in the umbonal region. Beak 

 small, incurved over the one of the opposite valve, and obliquely- 

 truncated. Foramen small. Sinus absent, generally not repre- 

 sented even by a slight depression at the anterior end. 



Brachial valve uniformly convex except at the posterio- 

 lateral angles where it is slightly flattened. Fold absent. Beak 

 small, inconspicuous. 



Surface marked by concentric, imbricating lamell?e which 

 give rise to successive rows of minute, flat spines. 



^ 



Fig. 15. — Cleiothyris hirsuta. A dorsal view showing some of the flat 

 spines which have escaped removal, enlarged three diameters. 



Length and width of average-sized individuals lo mm. ; a 

 larger crushed specimen reached 14 mm. in length and width. 



In the Maxville specimens the posterior margin is more 

 nearly straight than it is in the ones figured by Whitfield, so 

 that the greatest width of the shell is nearer the posterior end. 

 The spines are more or less removed leaving commonly only 

 the concentric lines. 



The species is readily recognized by the concentric rows 

 of flat spines. 



Horizon and locality. — Maxville limestone. 

 Undetermined zone : Harper Shaft, Olive Furnace. 



