30 Field Columbian Museum — Geology, Vol. II. 



anterior prolongation the angular, as does Baur. From the fact 

 that the bone on the inner side of the dentary, covering Meckel's 

 groove, is the only one which can with propriety be called "splenial" 

 (a " bandage " or "patch "), or opercular (a cover), it will be better to 

 retain the former name for the element, as usually applied, and to 

 give a new name to the part separated from the articular, wherever 

 it exists as an independent bone; it may be called the prearticnlar. 



AAi JAAAJlAJJM 



Fig. 4. 



Riylit mandible of Clidastes tor/or Cope. D.. dentary; s/>., splenial,- pra.. prearticnlar; <mg. x 

 angular: air., coronary; art., articular; sin., surangular. 



I assume that the element containing the cotylus must be the 

 articular, and that the one in front of it, back of the coronoid and 

 dentary, must be the surangular, though, as already stated, I can find 

 no positive evidence of a separating suture in the present specimen, 

 as is also the case in the adult Sphenodon mandible. Doubtless in 

 some more fortunately preserved specimen, or in one of a younger 

 animal, the separating suture will be traced. I will add that the 

 suture indicated by Cope* in his figure of the skull of Cimoliasaurus 

 snowii, as separating the articular from the surangular, does not exist 

 in the specimen; the place is indicated by a mere groove only. 



The angular is very long, and is extensively visible from both 

 within and without. On the outer side it is seen reaching to a little 

 beyond the proximal end of the symphysis, where the pointed extrem- 

 ity is visibly intercalated between the dentary and a small portion of 

 the splenial. On the inner side, the suture follows inward below the 

 cotylus to the anterior inner angle of the articulation, near which it 

 passes upward to meet the prearticnlar. The bone passes beneath 

 this latter.t'ltment but its connection with the surangular cannot be 

 made out. Along the inferior border of Meckel's groove and the 

 splenial, the suture goes forward to near the proximal end of the 

 symphysis. 



On the inner side of the mandible, there is an extraordinary 

 arrangement of the bones. After much deliberation, I interpret them 



*Proc. Ani.-r. Phil. Soc. 1894. 



