66 PALEOZOIC FISHES OF NORTH AMERICA. 
Up to the present time no teeth have been found associated with these 
spines, except those of Rhynchodus, and we may suspect that they belong 
together. If this were true, it would be strange that no similar spines have 
been found with the very numerous teeth of Rhynchodus in the Cornifer- 
ous limestone of Ohio. 
H&ETERACANTHUS POLITUS, Nn. sp. 
Plate XXI, Figs. 4, 5. 
Spine eight to ten inches long, compressed laterally at base, which is 
obliquely rounded below; summit curved forward, conical, with a subtri- 
angular section. Anterior margin uniformly arched, sides flattened toward 
the base, lower two-thirds of posterior face open; upper third flattened; 
sides of unequal breadth, making the spine unsymmetrical. 
The want of symmetry of these spines as well as their reversed curve 
renders it almost certain that they are the defenses of the pectoral fins 
They resemble in these characters Physonemus, but are without tubercles of 
any kind, and have in the minutely sinuous sutures a character so peculiar, 
that I have given it generic value. 
Formation and locality: Cement beds of Hamilton age, Milwaukee, Wis. 
Collected by Thomas A. Greene. 
Crenacantuus Wricutl, Newb. 
Plate XXVI, Figs. 4-4*. 
Ctenacanthus Wrighti, Newb., Thirty-fifth Rept. N. Y. State Museum, 1884, p. 206, pl. 
16, fig. 12-14. 
Spine of large size, long-triangular in outline; anterior margin straight, 
laterally compressed; medullary cavity large, open posteriorly to the middle 
of the spine; posterior surface traversed above by a strong rounded ridge ; 
denticles small; surface of exposed portion entirely covered with closely 
pectinated ridges of nearly uniform width on the front and sides, becoming 
narrower and less distinctly pectinated near the posterior margin. 
The spines of this species are very striking in their characters as regards 
both form and markings. The anterior margin seems to have been abso- 
lutely straight from base to summit. Along the line of junction between 
