Apr. 1903. North American Plesiosavrs — Williston. 



3i 



as the splenial (presplenial of Baur), the prearticular (angular of 

 Baur), and the coronoid. The identity of the splenial is assured. It 

 has been dislodged upward slightly, disclosing the narrow Meckelian 

 groove, which terminates in an orifice at the proximal end of the 

 splenial. The bone ends posteriorly below the coronoid eminence. 

 Anteriorly it broadens so as to cover all but the upper inner part of 

 this surface, uniting with its mate to form the symphysis. From 



AA&A LA-JLJU^ h 



Fig. 5. 



Left mandible to symphysis of Doliehorhynehops osbomi. ar/., articular; /m., prearticular; 



<!ir.. surangular; cor., coronary; sf., splenial. Compare also Fl. II. 



below, the thickened bone forms the inner part of the symphysis for a 

 short distance forward, at least. How far it extends can not be deter- 

 mined, as it gradually becomes thinner and disappears from view. 



PI. II.) 



The bone which I determine as the coronoid .is most peculiar, 

 remarkably unlike that in any other animal which I know. It is a 

 long, slender, flattened, trihedral bone, extending far forward, and 

 like the splenial, meeting its mate in the median symphysis. It 

 extends as far back as the end of the dentary, along its inner side, to 

 tin- most elevated part of the surangular, where it is thin and spatu- 

 late. It follows the inner margin of the dental border of the dentary, 

 apparently at least as far as the middle of the symphysis. At the 

 beginning of the symphysis with its mate, the bone is somewhat tri- 

 angular in cross-section, with its thin margin below touching the 

 splenial; the mesial surface is in contact with that of its mate, while 

 the upper surface is narrow. On one side the bone, while still retain- 

 ing its proper relation with that of the opposite side, has been par- 

 tially dislocated from the mandible, so that there can be no question 

 of its morphological relations to the contiguous elements.* 



Between the splenial and the coronoid, on the inner side, is 

 seen a narrow, thin bone, corresponding epiite to the dermogenous 

 portion of the articular in the turtles and Rhynchocephalians, that is, 



♦This peculiar relation' of the coronoid is well illustrated in fie. 13, P-476. vol. xxxvii, of the 

 Quarterly Journal of the Geological Society, in Prof. Sollas' article on "A New Species it 



1 mrus from the Lower Lias of Charmoiitli." 



