A Preliminary Description of the Opercular 

 and other Cranial Bones of Xiphactinus 



Leidy, 



Contribution from the Faleontoloo;ical Laboratory, No. 40. 



BY ALBAN STEWART. 



With Plates X, XI. 



In the museum of the University of Kansas there is one specimen 

 of Xiphactinus that has the opercular bones in ahiiost complete 

 condition, and another partially so. As these bones, with the ex- 

 ception of the preopercular, have never been described from com- 

 plete' specimens I think it will be well to give a short description 

 of them with figures. The catalogue number of the specimen under 

 consideration is 88. 



The opercular is a broad, flat plate of bone, near the anterior 

 superior portion of which there is a deep elliptical pit for articu- 

 lating the bone with the hyomandibular. This pit is projected 

 rather outward from the rest of the bone, very closely resem- 

 bling the corresponding portion of Saiirodon in this respect. Just 

 above this pit there is a sharp angular projection at the point 

 where the anterior and superior borders meet, but I am inclined to 

 think that this character will not be constant in all specimens. 

 From this point the superior border extends backward and down- 

 ward in an irregularly curved line to the lower border, which is 

 less curved and somewhat striated just above it. The anterior 

 border, extending from the articular portion just mentioned down- 

 ward, is nearly straight and somewhat thickened. Back of this 

 border the bone is very thin, thus making it difficult to collect in 

 perfect condition. 



The preopercular is a somewhat triangular-shaped bone with a 

 very thick and concave anterior border. The lower portion of this 

 border is directed forward at quite an angle and is received in a 

 slight groove on the back portion of the quadrate. Extending 



(19) KAN. UNIV QUAR., VOL. VIII. NO. 1, JAN. 1899, SERIES A. 



