"Williston.] Mosasaurs. 205 



Clidastes westii. 



Clidastes westii Williston and Case, Kans. Univ. Quart., i, p. 29, 1892. 



The specimen upon which this species was based consists of 

 a complete lower jaw, quadrate, fragments of the skull, the 

 larger part of the vertebral column, and the incomplete hind 

 and fore paddles. The vertebras preserved are in two series, 

 the one, numbering thirty-three, continuous with the skull ; the 

 other, sixty-three in number, all chevron caudals. The termi- 

 nal caudals preserved indicate that there were several more in 

 life, perhaps eight or ten ; the first of the series was evidently 

 among the first of those which bore chevrons. Altogether, the 

 tail may have had seventy-five chevron caudals. The length 

 of the two series are respectively seventy-one and seventy-two 

 inches. Assuming that there was the same number of precau- 

 dal vertebrae as in Clidastes velox, the entire vertebral column 

 would have measured in life fifteen feet and four inches. The 

 lower jaw shows the skull to have been very nearly twenty-four 

 inches in length, giving a total length for the animal when 

 alive of seventeen and one-half feet. It is thus seen that the 

 species is one of the largest of the genus. 



While the skeleton was only about one-half longer than that 

 of C. velox described in the foregoing pages, or of about the same 

 length as a very complete specimen of C. tortor in the museum 

 collection, the proportions of the animal were very much stouter. 

 The figures given in plate liii of the twenty-fifth, or eigh- 

 teenth dorsal, vertebra will show the proportions between length 

 and breadth. It is upon these remarkably stout proportions, 

 and the shape of the articular faces as indicated by the figures 

 and the measurements appended, that the species is chiefly dis- 

 tinguished from those previously known. The articular sur- 

 faces of the basal caudal vertebras are remarkably triangular in 

 shape, with the angles rounded and the sides of nearly equal 

 length. This triangular shape is persistent for the first twenty 

 of the series as they are preserved. The paddles, as shown in 

 plates xxxv and xxxvi, show much stouter proportions than in 

 any other known species. 



