276 University Geological Survey of Kansas. 



of this border the bone is very thin, thus making it difficult to 

 collect in perfect condition. 



The preoperculum 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 re- 

 ceived in a slight groove on the back portion of the quadrate. 

 Extending backward from the extremity of this portion there is 

 a row of large, shallow foramina, the posterior ones of which 

 have shallow grooves leading into them from behind. Below 

 this line of foramina the bone is not so thick, and is covered 

 with numerous fine strise. The superior portion has a rather 

 broad process extending upward, formed by the anterior and 

 superior borders. The posterior portion of the bone is thin and 

 striate on both sides of the upper portion. 



There is still another opercular bone, which I regard as a 

 suboperculum. The bone is broad and flat, thin along the bor- 

 ders, and thickened toward the central portion. The posterior 

 extremity is the broader of the two and is somewhat rounded. 

 The anterior end is much more narrow and bears a small ellip- 

 tical facet on a slight elevation of the bone. It also presents a 

 beak-like process, separated from the above by a slight depres- 

 sion. Both the external and internal sides are striated, the 

 striae becoming very pronounced near the posterior end of one 

 of the sides. Measurements of the opercular bones are : 



Operculum : Length of the anterior border * 373 mm. 



Length of the anterior border below facet for the 



hyomandibular 268 " 



Length of facet for the hyomandibular 55 " 



Transverse width of facet 22 " 



Preoperculum : Greatest length * 345 ' ' 



Width near superior extremity 80 " 



Width of inferior end * 170 " 



Subopercular : Total length 290 " 



Width across anterior extremity * 90 " 



Width across posterior extremity * 146 " 



There are four other bones, some of which are fragmentary, 

 which are figured on plate XLIV. They were all found in con- 

 nection with the skull and evidently belong to it. The first of 

 these bones, figs. 1 and 5, is an elongated bone, expanded at 



* Estimated. 



