c 2 NATURAL HISTORY BULLETIN. 



The disk is nearly round and evenly swollen, without any 

 abrupt rise over the arms; the granulations, in fact, extend 

 out a little on the arms. The whole surface, above and be- 

 low, is uniformly covered with small, smooth, rounded gran- 

 ules. On some portions there are, also, a few scattered, 

 slender, acute smooth spines, as figured. Radial shields are 

 not even indicated by ridges. Under the granules are very 

 small scales. The arms are narrow and high, with a slight 

 dorsal carina. They are not beaded, for the side arm-plates 

 project but little. The rows of spines do not approximate 

 dorsally. The upper arm-plates are thick, elevated, about as 

 wide as long, five-sided, or on some joints six-sided; the outer 

 end is widest and is prominent, in the middle, where it is ob- 

 tusely angulated, or often slightly truncated. The proximal 

 sides are nearly straight and convergent; the inner end is 

 narrow and truncated, and in contact with the preceding 

 plate. 



The oral shields are nearly broad "heart-shaped," but 

 without any notch in the outer end, which is broadly round- 

 ed with a slight median angle, and has a row of twelve or 

 more small granules along its margin; the inner sides are 

 slightly incurved; the acute inner end extends far inward on 

 the jaws. 



The adoral plates are narrow and long, and do not meet 

 proximally; they are three-lobed; one of the distal lobes joins 

 the first arm-plate; the other is very narrow and extends out 

 between the oral shield and the first side arm-plate, slightly 

 separating them. In Mr. Lyman's figure these parts are left 

 indefinite. The whole surface of the jaw, proximal to the 

 oral shields, is covered with a close group of granules, some 

 of which are conical and similar to the mouth-papilla? and 

 tooth-papilla? alongside of them, so that they are liable to be 

 confounded. Of true mouth-papilla? there are either five or 

 six on different jaws, besides a more distal short oral scale. 

 The two outer mouth-papilla? are larger and broader than 

 the rest; they may be ovate or obovate, flat, obtuse, or sub- 



