FOSSILS OF THE BURLINGTON GROUP. 427 



tweon the arms, but their exact arrangement cannot be 

 made out from the specimen studied. 



Anus, after their origin on the second radials, each bifur- 

 cating on the sixth piece (excepting those of the anterior 

 ray, which divide first on the eleventh piece), the inner di- 

 vision of each being smaller than the other, and remaining 

 simple; while the outer or main arm gives off another di- 

 vision on the inner side on the eighth piece above the first 

 bifurcation, and still another on the ninth or tenth piece 

 above the latter, which is as far as the arms can be clearly 

 traced in the specimen, though there is some appearance of 

 a fourth bifurcation in one of the arms. Arm pieces short, 

 or from twice to three times as wide as long, and not in 

 the slightest degree wedge-shaped; each with lateral edges 

 sharp and a little projecting, and provided with a little 

 pointed process on the middle of the dorsal side. These 

 little asperities, and the beveled character of the sutures 

 between the arm joints, give the arms a rough, rasp-like 

 appearance, which has suggested the specific name. The 

 body plates are also rendered very rough by a ridge extend- 

 ing from the middle of the upper edge of each first radial 

 to connect with others on the subradials, and the presence 

 of other irregular asperities. Sutures between the first and 

 >r-ond radials widely gaping when the arms are folded to- 

 gether. Column of moderate size, and composed of thin, 

 nearly round pieces, with projecting rough edges, and a 

 rather small subpeutagonal central perforation. 



Hight of body to the top of the first radials, 0.10 inch ; 

 breadth, about 0.42 inch; length of arms, about 1.70 inches. 



This species is related to Ztacrinns peranyulatux, of Dr. White, but 

 differs in having- its arms longer and less tapering, as well as bifurca- 

 ting more frequently : also in having- each inner division of each arm 

 smaller than the outer. The bifurcating pieces of its arms are likewise 

 proportionally smaller, and not protuberant as in that species. In the 

 species iH-ranyulatm the arm pieces are also merely angular along the 

 middle, while in that under consideration there is. iu stead of a coiitinu- 



