AVilliston.] Mosasaurs. 201 



roughening, as in C. velox, and of which there is no sign in 

 the specimens of other species at my command. The rugosity 

 below the stapedial process is confined to the outer side, as in 

 velox, and the length of the process is the same. The shape of the 

 distal articular face presents no tangible differences. Further- 

 more, C. velox and the present are the only species of the genus 

 now known in which the coracoid is emarginate ; the two spe- 

 cies agree in the paddles quite, and no two other species do. 

 Finally, there are specimens in the museum which are inter- 

 mediate in size between the two. 



Taking all these facts into consideration, I am still of the 

 opinion that there is but a single species. 



Clidastes tortor. 



EcJpstosaurus to)'torCope, Proc. Amer. Phil. Soc, Dec. 1871. Marsh, Amer. 

 Journ. Sci., in, 261, April, 1872. 



Clidastes tortor Cope, Cret. Vert., etc., pp. 48, 265, pis. iv, f. 1; xiv, f. 2; 

 xvi, ff. 2, 3; xvii, f. 1; xix, ff. 1-10: xxxvi, f. 3; xxxvn, f. 2. Bull. U. S. 

 Geol. Surv. Hayden, in, p. 583. Williston and Case, Kans. Univ. Quart., i, 

 25. 



Edestosaurus dispar Marsh, Amer. Journ. Sci., June, 1871: June, 1872, pi. 

 i, ff. 1, 3. 



Edestosaurus rex Marsh, op. cit., June, 1872, pi. n, f. 1. 



Clidastes medius Merriam, Ueber die Pyth. der Kans.-Kreide, 35. 



The material referred to this species in the University of 

 Kansas consists of one nearly complete skeleton and the incom- 

 plete remains of five others. The descriptions given are taken 

 almost exclusively from the complete specimen, which was col- 

 lected by the late Judge E. P. West. The species appears to 

 be the most common of this genus in the Kansas chalk. I be- 

 lieve that I recognize three synonyms of the species in those 

 previously described. 



Edestosaurus dispar was the type of the genus. Its characters, 

 both generic and specific, were given together, as is the custom 

 of the author. The essential characters given by him, that is, 

 those not common to other species, are as follows : 



"In the cervical and anterior dorsals the cup and ball are 

 somewhat inclined : in the posterior dorsals and lumbars 

 [pygals] less so, and in the anterior caudals they are nearly, 



