204 PALEOZOIC FISHES OF NORTH AMERICA. 
One marked feature in this and the Scotch specimens is a peculiar 
prominence or flattened knob on the posterior margin considerably below 
the teeth. In its circular section, its central pulp cavity, its smooth and 
polished surface, and single row of relatively large recurved denticles, this 
spine resembles Compsacanthus levis, N., from the Coal Measures of Linton, 
Ohio,! and it is possible they should be included in the same genus. 
To permit comparison between the American and Scotch specimens [| 
give herewith (Pl. XXI, Fig. 11*) a copy of Dr. Traquair’s drawing of the 
spine lately found in Scotland. 
SanpaLopus crassus, N. & W. 
Plate XXI, Figs. 6-8. 
In the Report of the Geological Survey of Illinois, vol. 4, p. 369, PL IV, 
Fig. 3, I described and figured a fish tooth received from Dr. A. Litton, of 
Saint Louis, to which the above name was given. This tooth was imperfect, 
lacking the narrow anterior extremity and the extreme posterior angle. I 
have recently received from Mr. William McAdams, of Alton, a number of 
perfect teeth of this species, which show that the figure referred to above is 
liable to convey a wrong idea of the complete form. For this reason I have 
thought it best to give herewith two figures of these teeth as found in their 
most perfect condition. One of these, represented in Fig. 7, shows the 
crown essentially perfect, and but for the information afforded by that 
shown in Fig. 6 it would be regarded as a perfect tooth. From this latter, 
however, we see that when absolutely perfect the crown carries a narrow 
beveled margin from the middle of the straight side down to the posterior 
angle, and it is there prolonged into a prominent acute point, one-quarter 
of an inch or more in length. In all others of the great number of speci- 
mens which I have seen this point is broken way, but many of them show, 
more or less plainly, the beveled border separated from the crown by a dis- 
tinct line of demarkation. This margin was evidently covered by integu- 
ment, and the point formed by the prolonged angle doubtless served to 
increase the firmness of the ligamentous attachment of the bony teeth to 
the cartilaginous jaw. 
1 Paleontology of Ohio, vol. 1, p. 332, pl. 40, fig. 5. 
