188 PALEOZOIC FISHES OF NORTH AMERICA. 
Order CROSSOPTERYGID£. 
CCELOSTEUS, nov. gen. 
Fishes of large size allied to Dendrodus and Rhizodus. Only a coracoid, 
mandible, and tooth have yet been found, but these certainly represent a 
fish generically different from any before met with on this continent. The 
bones are peculiar in their structure, consisting of a thin shell of dense 
osseous tissue, inclosing large cavities, once doubtless filled with cartilage. 
In this respect they resemble the bones of Dendrodus and contrast strongly 
with those of Dinichthys and the allied genera of Placoderms, Titanichthys, 
ete. In Dinichthys the coracoid is a bone nearly as large as one’s arm and 
haif as long, composed of dense bone-tissue throughout. The correspond- 
ing bone in Celosteus is about a foot in length and an inch and a half in 
diameter at the middle, and the central cavity is as large, relatively, as in 
the long bones of birds; the shell which surrounded it being but from one- 
eighth to one-quarter of an inch in thickness. 
The dentary bone is about one foot in length, two and one-half inches 
wide in the middle, where it is one and a quarter inches in thickness, and 
four inches wide at the posterior end, where it was doubtless joined to the 
angular and articular elements. On the outside the posterior half is exca- 
vated to form a deep sulcus for the reception of the motor muscle, which 
must have been of unusual power. On the inside the jaw is flattened and 
gently arched downward to the rounded lower edge. The upper side bears 
on the outside a subacute toothless ridge; within and below this is a wide. 
shoulder with seven broad and shallow pits,in which were planted the 
rounded bases of large, conical teeth This is a structure in some respects 
similar to that of the mandible of Dendrodus, but the jaw of Celosteus is 
much broader posteriorly, having a triangular outline like that of Améa, and 
has as its most striking feature the deep sulcus to which reference has been 
made above. The exterior surface of the jaws of Dendrodus is also strongly 
tuberculated, whereas in Calosteus it is smooth or coarsely striated longi- 
tudinally. The dentition, too, differs in a marked degree from that of Den- 
drodus, in which a row of closely set teeth of small size crown the upper and 
