No. I.] THE GENUS OF FOSSIL FISHES. 37 



on the inside of the ramus to beyond its middle. A lower jaw 

 of Xiphactinus (No. 3782, U. S. N. M.), in almost perfect 

 condition (Fig. 5), enables me to correct some of these state- 

 ments. Cope's articular is not short, but its continuation for- 

 ward forms the long sword-shaped process that he regards as 

 belonging to the "angular." In short, this articular corre- 

 sponds to the autarticulare of Van Wijhe {Nicderldnd. ArcJiiv. f. 

 ZooL, vol. V, pp. 207-320) and originates from the ossification 

 of Meckel's cartilage. Cope's angulare is not the true angu- 

 lare, but is Van Wijhe's dermarticulare, a membrane bone. 

 In Lepisosteus, Amia, and Polypterus these bones remain 

 distinct. Van Wijhe {pp. cit., pp. 306, 307) makes the follow- 

 ing statement in speaking of the elements of the lower jaw of 

 the genera mentioned above : " Eine Vergleichung mit den 

 Teleostiern zeigt, dass was bei diesen als Articulare angegeben 

 wird durch eine Verschmelzung des Autarticulare mit dem 

 Dermarticulare entstanden ist." Here, however, in this Cre- 

 taceous genus of Teleosts, we find these elements still distinct 

 from each other. In the genera of so-called Ganiods referred 

 to above the autarticulare is very short ; but, relying on two 

 good specimens of Xiphactinus and one of Ichthyodectes, I am 

 confident that the proximal end of the autarticulare is continu- 

 ous with the long sword-shaped process described by Cope, and 

 that this process is entirely distinct from the dermarticulare. 



If the true angulare ever was present in Xiphactinus, it has 

 become consolidated with the dermarticulare. In a specimen 

 of Ichthyodectes there is present a surface to which an angulare 

 seems to have been sutured. Crook represents it as present. 



Professor Cope's figure of the lower jaw of Xiphactinus 

 {Cret. Vert., PI. XXXIX) at first sight gives one the impression 

 that the rounded head of the quadrate articulated with a similar 

 rounded head belonging to the lower jaw. The latter, how- 

 ever, is the " prominent angle, like half of an ellipse," and the 

 quadrate was supposed to enter its cotylus mesiad of this 

 angle and well forward. My Fig. 5 shows the jaw seen from 

 within. The cotylus is furnished partly by the autarticulare 

 and partly by the dermarticulare. The head of the quadrate 

 sits in its cotylus on the mesial side of the broad process of 



