264 New Species of Crinoidea from the 



having nodose plates of body and dome, and in the im- 

 portant distinction of having four arms to each ray, in- 

 stead of five in the postero-lateral rays, as in that spe- 

 cies. 



Geological formation and locality. Burlington lime- 

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

 Bvrlingion. 



Actinocrimis opusculns ( n. s. ). ( A. ojuisculus. 1st 

 Supp. to Geol. Rep. Iowa, Explan. of pi. 2, fig. 6.) Body 

 broadly caliculate, height little more than half the width, 

 the brachial plates spreading around the circumference of 

 the cup in the form of a rim ; base truncate, and largely 

 excavated for the attachment of the column. Basal plates 

 short, thickened at the outer margins, and indented at the 

 suture lines. First radial plates wider than high, with 

 long upper lateral sides. Second radial plates quadrangu- 

 lar and pentangular, wider than high. Third radials larger 

 than the second, varying from pentagonal to hexagonal 

 and heptagonal, very obtusely wedge-form above, and sup- 

 porting on each upper sloping edge a large bifurcating 

 supra-radial plate ; these each support upon the outer edge 

 a series of brachial plates, and upon the inner edge a su- 

 pra-radial plate of the second order, which gives origin to 

 two arms, making six arms to each ray, and thirty arms to 

 the whole. 



Interradial series consisting of four or five plates each, 

 the first one seven or eight sided, supporting two in the 

 second range, one six and the other seven sided, and one 

 or two small plates in the third range. First anal plate 

 hexagonal, about equal to the first radial, supporting two 

 or three slightly smaller plates in the second range, with 

 two to four irregularly placed above. The interradial and 

 anal spaces are inclosed or arched over by the brachial 

 plates. Surface of plates strongly convex, traversed by dis- 

 tinct ridges, which, passing from the centre of the plates, 

 unite at the edges with those of the adjoining ones. 



