54 PALEOZOIC FISHES OF NORTH AMERICA. 
erous limestone. Figures and descriptions of these teeth are given in an 
article on the fossil fishes of North America.’ As they are generally found 
detached, nothing was known until recently of their relation to any other 
fish remains found in the Corniferous limestone, and as the most abundant 
eranium in this rock is that of Macropetalichthys, it was suggested that they 
formed part of the dentition of that fish After a time, however, some of 
these teeth were found associated together in rows of seven; an arrange- 
ment most like that of the teeth of Sharks. And as they seem to have been 
connected with their basal support by only ligamentous attachment, as the 
teeth of Sharks are attached to their jaws, this circumstance was regarded 
as confirmatory evidence of their Selachian character. It happened, how- 
ever, in several instances that plates of various forms, maxillaries and man- 
dibles set with teeth and numerous scales—each group evidently the frag- 
ments of a single individual—were found on slabs taken out of the quarries 
at Sandusky and Delaware. Among these fragments there was almost 
invariably a single series of the teeth of Onychodus. How to establish a 
relationship between these teeth and the associated remains, which were 
those of a well-marked Ganoid fish, was for a long time a puzzle; but by a 
fortunate discovery of Mr. Hertzer the problem was at last solved. He 
found at Delaware a large dentary bone of Onychodus, to which the peculiar 
series of large teeth are attached in their normal position; that is, be- 
tween the extremities of the mandibles, where they hold the position of the 
median row in the dentition of a Shark. They are attached to a bony 
arch, from which they radiate. This is inserted in the symphysis of the 
jaw, supported by a shoulder on the internal face of the extremity of each 
mandible. 
So far as we yet know, there are no corresponding or interlocking 
teeth in the upper jaw; and hence it would seem that they armed the pro- 
jecting extremity of the under jaw, just as the steel point arms the prow of 
a steam ram. We shall probably find more perfectly preserved specimens, 
which will fully explain this apparently anomalous structure, and perhaps 
correct in some degree our conclusions in respect to it; but the specimens 
1 Notes on American Fossil Fishes; Am. Jour. Sci., 2d series, vol. 34, 1862, p.73; also described in 
Bull. National Inst., Jan., 1857, 
