Carboniferous Rocks of the Mississippi Valley. 269 



pearance of the teeth of a file. The tentacula are long 

 and slender, composed of numerous joints, each of which 

 has, on its outer edge, a strong, sharp, curved spine, in- 

 clined obliquely outwards and upwards. Column com- 

 posed near the body of alternately thicker and thinner 

 joints, every fourth of which is larger, and projects beyond 

 the others as a carinated ring. 



In the specimen examined only the lateral rays are 

 determinable ; but the peculiar character of the arms is 

 sufficient to distinguish this from every other described 

 species. 



This species most resembles A. spinotentaculus, but dif- 

 fers in the number of arms to the ray, the teeth-like ridges 

 of the arm plates, and the single series of plates near the 

 arm bases. The arms of several other specimens are 

 known. 



Geological formation and locality. Burlington lime- 

 stone, Burlington, Iowa. Collection of C. A. White. 



Actinocrinns reticulatus (n. s.). Body broad, sub-tur- 

 binate, truncate at base, and deeply excavated for the 

 attachment of the column. Basal plates short, thickened 

 at the lower margins, and projecting downwards over the 

 top of the column. First radial plates of medium size, 

 little wider than high, the upper lateral sides very long. 

 Second radial plates smaller, wader than high, hexagonal, 

 except in one postero-lateral ray, where it is quadrangular. 

 Third radial plates hexagonal or heptagonal, usually equal 

 to the second radials, supporting on each upper inclined 

 side a supra-radial plate ; this is wedge-form above, and 

 supports on each side a series of brachial plates, except in 

 the anal portion of the postero-lateral rays, where there is 

 an additional supra-radial plate of the second order on the 

 inner margin of the first supra-radial plate, giving three 

 arms to that portion of the ray ; making the brachial formula 

 II = 22. 



