VERTEBRATES. 123 



base 6 lines, thickness 1 line ; concave margin acute, and set 

 with a line of relatively large tubercles ; convex border acutely 

 carinated, without tubercles but finely striated longitudinally; 

 lateral surfaces bearing numerous small, round, smooth tuber- 

 cles, near the concave border, densely crowded and without 

 linear arrangement, toward the convex border, especially 

 below, they are also numerous, though less crowded than along 

 the opposite edge, their nearest margin forming about three 

 longitudinal lines. Those more remote are smaller and are 

 dispersed in short, transverse lines. The median half of the 

 lateral surface bears only a few minute tubercles, and like all 

 the other portions of the surface between the tubercles is finely 

 striated longitudinally. The position, size and form of the 

 pulp cavity is scarcely determinable from the only specimen 

 before us. It is apparently situated, however, nearest the con- 

 vex border. The ornamentation of the surface descends much 

 lower on the concave than on the convex border ; the line lim- 

 iting the ornamentation — the line of junction with the surface 

 of the back — rising from the concave toward the convex bor- 

 der at an angle of about 45°. 



The resemblance of this spine to some species of Oracanthus, both in general 

 form and ornamentation, is so strong that, were it not for the fact that the line 

 of junction with the dorsal surface was inclined upward from the concave edge, 

 we should scarcely dare separate it from them. 



Formation and locality: Coal Measures, Springfield, Illinois. 



Drepanacanthus gemmatus, N. and W. 



PI. XIII, Fig. 1. 



Spine large and strong, 10 to 12 inches in length, one in 

 width at base, gradually narrowed to the apex, which is 

 strongly curved forward, much compressed throughout, section 

 near the base a long ellipse, truncated anteriorly, nearer the 

 summit the sides are flat and parallel, the anterior border 

 rounded, posterior margin occupied by a broad and shallow 



