STEWART: CRANIAL BONES OF XIPHACTINUS. 21 



Subopercular?; total length 290 " 



" width across anterior extremity 90* " 



" with across posterior extremity 146* " 



Cerato-hyal; greatest length 238 " 



" width across anterior end 86 " 



'•■ width across posterior end 97 " 



There are four other bones, some of them are fragmentar}', that 

 I have never seen figured or described before;")" figures of which are 

 shown on plate XI. They were all found in connection with the 

 skull, and evidently belong to it, with the probable exception of 

 one. The first of these, Figs, i and 5, is an elongated bone, ex- 

 panded at one end and contracted into an elongated, narrow, and 

 somewhat thickened process at the other, at the extremity of which 

 there is a roughened surface which probably gives attachment for 

 cartilage. On one side of this process there is a long, thin lamina 

 of bone, extending toward the extremity and so closely applied to 

 it that at first sight it has the appearance of being the border of a 

 groove on the edge of the process. The expanded end is thickened 

 and bears a small articulating surface, the face of which is almost 

 in line with the process mentioned above. 



The second of these, Fig. 2, is represented by portions of two 

 bones. These are thin on one side while the other is much 

 thicker and has a shallow grove, formed by an overhanging 

 ridge of bone. This thickened portion was probably continued 

 outward in a process beyond the rest of the bone. The third. Fig. 



3, is plate-like and more or less sculptured on both sides. On one 

 of the sides there is a broad, triangular-shaped depression, which is 

 invaded by a notch from the edge of the bone, and on the side there 

 is a prominent ridge extending awa}' from the apex of this notch. 



I have found a bone almost identical with this in connection with 

 the opercular of an unknown fish, which evidently does not belong 

 to the Satirodontidcv, and with this fact in view it must be referred 

 to this genus with doubt The fourth and last of these bones, Fig. 



4, may be an infra-opercular. It is the largest of the bones under 

 consideration, and is very thin and flat, excepting on one of the 

 sides, where it suddenly thickens into a prominent ridge, which 

 probably continues to the border. The bone is finely striated on 

 both sides. 



Lawrence, Kas. , Jan. 6, i8gg. 



♦Estimated. 



+Since the above articl'- has gone to press I find that two of the bones described 

 above, platexi, figs 1, 3, and .5. have been figured by Prof. Cope, Cret. Vert. West., pi. 

 XL, figs. 4. 4a, and 8. The last of these is called an ■'uncertain bone," and the first a 

 "Hyomandibular," which, of course, is incorrect. 



