308 University Geological Survey of Kansas. 



of a broad, thin posterior plate and the malleolar portion. 

 This latter is somewhat deeper than in Ichthyodectes acanthicus, 

 and does not have a tuberosity on the external side. The two 

 portions of the bone are separated by a constricted neck. 

 Nothing more can be said of the mesopterygoid than that it is 

 a very thin bone. 



The quadrate is very deep, as might be expected from the 

 corresponding depth of the mandible. The upper portion is 

 very thin and has a slight groove on the internal side for the 

 symplectic. The condyle is very convex and directed well for- 

 ward. The upper border seems to be nearly straight and prob- 

 ably unites with the metapterygoid in a manner similar to that 

 found, in Xiphactinus. The preoperculum is very thin, broad 

 below, and narrow above. 



The ethmoid is very similar to this bone in Xiphactinus and 

 Ichthyodectes, being formed into a beak anteriorly, and thin, and 

 united with the frontals by a dentate suture posteriorly. The 

 frontals are separated by a well-marked non-dentate suture, 

 w^hich is shown throughout its length in one of the specimens. 

 Over the orbital cavities the bones are somewhat thickened, and 

 evidently gave attachment to a chain of supraorbital bones, as 

 in Xiphactinus. Posteriorly they unite with the postfrontals, 

 parietals, and probably the pterotics. 



As there has been some doubt as to the exact position of the 

 parietals and pterotics, I quote the following paragraph from 

 Professor Hay, 67 which seems to me to be the correct explana- 

 tion of these parts : 



"Crook has interpreted the bones of the posterior upper re- 

 gion of the skull of his I. polymicrodus as he has those of Por- 

 theus (Xiphactinus) ; but, as in the case of the latter, I am 

 compelled to differ with him. However, many of the sutures 

 are very difficult to demonstrate. According to Crook, the su- 

 praoccipital is greatly expanded in front, while the parietals lie 

 laterad to the epiotics. It seems to me that the supposed ex- 

 panded portion of the supraoccipital is really the area belong- 

 ing to the parietals. There is a very distinct fold running along 



67. Amer. Jour. Sci., vol. VI, p. 230. 



