AND AVES OF NORTH AMERICA. 



187 



covered. In the following cuts the outlines of the proximal extremities of the ossa quad- 

 rata are given, with sections at a little below the middle of the length of each. 



Fig. 48. 



1. Mosasaurus maximus, Cope. 5. Liodon validus, Oope, position (Re reverse of the. pthers. 



3 - " dekayi, Broun. o. ciidastes propython, Cope. 



"• depressus, Cope. One^third natural size. The great alae in 2a and (5a are 



4. Plateoarpus tympanitious, Cope. unknown. 



b, the great ala; e, the meatus auditorius; d, the posterior deeurved extremity of the proximal end of the os 

 quadratum. 



Dotted lines crossing the outlines indicate fractures and restorations outside of 

 them. In figs. 4a and (5a the dotted lines indicate the bridging of the meatus by the 

 proximal extremity of the bone. The great ala is lost in our specimens both of M. dekayi 

 and M. depressus. The marked peculiarity of M. depressus is shown above; also, the 

 great declinature of the superior extremity around .and behind the meatus in the Platecar- 

 pus and the Ciidastes. In them it descends below opposite the point of section and is 

 therefore divided by the line from which the outline is taken. In Mosasaurus minor, 

 gracilis, and brunibyi, the quadrate hone is unknown. 



Vertebrce. The outlines of the lateral elements of the atlas of five species, including 

 that of the giganteus, (from Camper) indicate corresponding differences, which are most 

 distinct on the internal faces. In M. giganteus, M. depressus, and M. dekayi there is 

 a facet for articulation with the centrum, just below the anterior facet. In order to ac- 

 commodate this, the inferior ala, ceases behind the anterior facet in the last two species, 

 or is only developed at the posterior part of the element in the European animal. In the 

 M. maximus, on the contrary, this ala is prolonged to, and even beyond the anterior or 



