INVERTEBRATES. 93 



angle of the dorso-lateral pieces. This is succeeded by a series 

 of radials so thoroughly anchylosed that the exact number can- 

 not be determined, two of which are protuberant, including the 

 axillary plate. One division of the ray probably divides again, 

 but the other remains single to its extremity. 



Column round, comparatively rather stout, and composed of 

 slightly projecting pieces. 



The specimen is silicious, and the surface markings, if any 

 existed, are thus obscured. 



Position and locality: Keokuk limestone. Keokuk, Iowa. 



Collection of Mr. L. A. Cox. 



CAT/'KorKi\rs TUXK'ATrs, Hall, sp. 



PI. XII, Fig. 6. 



Calyx less massive than in the preceding species, basal plate 

 triangular, and about twice as wide as high. Lower dorsal 

 plate short, or about three times as wide as high. Dorso-lateral 

 plate six-sided, with a strong constriction on ther outer lateral 

 borders, and their inner angles truncated above for the recep- 

 tion of the upper dorsal plate. This plate is triangular, about 

 twice as wide as high, and slightly protuberant. The three first 

 plates of the dorsal ray are shorter than the six succeeding ones, 

 which are a little wider than long, and slightly protuberant. 

 The ninth plate is axillary, and supports the arms, which ap- 

 pear to be simple to their extremities. 



Lateral rays five, of which only four are well preserved. First 

 radial series in these rays eight, including the long narrow series 

 that is arranged somewhat obliquely around the lateral sides of 

 the calyx. One or two of these in each ray, including the ax- 

 illary plate, are protuberant. Arms single above the first di- 

 vision on all the rays visible. 



We refer this form to the species described in the Thirteenth 

 Report to the Regents of the N. Y. University, under the name 

 of Cheirocrinm tunicatus. 



Position and locality: Keokuk limestone, Keokuk, Iowa. 



Collection of Mr. L. A. Cox. 



