265 



In Plalecarpus and CUdastes, the knob-ridge is low and ends obtusely 

 not far above the distal condyle, and the posterior alar is very prominent. In 

 Liodon, the knob-ridge is much more prominent, and forms a protuberant 

 angle below the position of the "knob" in Mosasaurus, which is continued by 

 a decreasing crest to the distal condyle. This ridge, with the equally prom- 

 inent posterior alar, causes a protuberance on the posterior part of the quad- 

 rate, between the meatus and the distal condyle, which is especially marked 

 in the Liodon validus. In the three genera mentioned, the position of the 

 median posterior. ridge is occupied by a concave surface. CUdastes planifrons, 

 Cope, is intermediate in the farm of its quadrate bone, between such forms 

 as C. torlor and the Platecarpi. Its internal angle and ridge are less promi- 

 nent than in C. tortor, and a part of it extends so near to the stapedial pit as 

 to have led me to call it the median posterior ridge in my original descrip- 

 tion, an error I now correct. Platecarpus tympaniticus is closely similar to 

 the Kansas species of the genus in the form of this element. 



In the following list are included a number of names of species which 

 I have not seen. Those described by Dr. Leidy and myself I believe to 

 be distinct from each other and from those described by the older authors. 



CLIDASTES, Cope. 



Proceedings of the Academy of Philadelphia, 1868, p. 233; Transactions of the American Philosophical 

 Society, 1870, 211. — Edestosaurm, Marsh, American Journal of Science and Arts, 1871, June ; Cope, 

 Proceedings of the American Philosophical Society, 1871, December. 



I. Frontal bones without median keel; dorsal vertebra depressed: 

 Clidastes planifrons, Cope. Plate XXII and XXIII, figs. 1-14. 



Hayden's Bulletin of the United States Geological Survey, No. 2, 1874, p. 31. 



Niobrara epoch, Kansas. 



II. Frontal bones with median keel; dorsal vertebra depressed : 

 Clidastes peopython, Cope. 



Proceedings of the Boston Society of Natural History, 18G9, p. 2!>8 ; Extinct Batrachia and 

 Eeptilia of North America, 1870, p. 221, Plate XII, figs. 1-21. 



Rotten limestone, "No. 4," of Alabama. 



Clidastes tortoe, Cope. Plates XIV, fig. 1 ; XVI, figs. 1,2; XVII, fig. 1; XIX, 

 ligs. 1-10; XXXVI, fig. 3; and XXXVII, fig. 2. 



Edeslosaurua torlor, Cope, Proceedings of tho American Philosophical Society, December, 

 1871. 



Niobrara Cretaceous of the Smoky Hill River. 

 34 c 



