THE KANSAS UNIVERSITY 

 SCIENCE BULLETIN. 



Vol. X, No. 5.] January, 1917. [vol'xx^no'I. 



Ogmodirus martinii, a New Plesiosaur from the Creta- 

 ceous of Kansas. 



BY S. W. WILLISTON, 

 Department of Palentologj', University of Chicago; and 



ROY L. MOODIE, 

 Department of Anatomy, University of Illinois, Chicago. 



THERE have been recorded from the Cretaceous deposits of 

 Kansas five genera and sixteen species of plesiosaurs, as 

 follows : 



From the Comanche (in the restricted sense of the term), two 

 species referred provisionally to Plesiosaurus; from the Benton, 

 two species of Trinacromerum (including the genotjrpe), one of 

 Brachauchenius, the genotype, and one of Elasmosaurus; from 

 the Niobrara, five species of Elasmosaurus, two of Polycotylus, 

 including the genotype, and one of Trinacromerum; from the Fort 

 Pierre, the genotype of Elasynosaurus, and one species referred 

 provisionally to Plesiosaurus. Of the above, doubtless all those 

 referred to Plesiosaurus belong to other as yet unrecognized gen- 

 era; and in much probability several of those referred to Elas- 

 mosaurus from the Benton and Niobrara will be found eventually 

 to pertain to other genera. One of these, especially E. ischiadicus 

 Will., quite surely does not belong in that genus and may belong 

 in the present genus. It was originally described as a proble- 

 matical species of Polycotylus because of its short cervical verte- 

 brae, but later quite surely eliminated from that genus because of 

 its short ischia. For the present it may find a location in the 

 following genus. 



The present genus, Ogmodirus, from the Cretaceous of Cloud 

 county, Kansas, is of peculiar interest in presenting certain in- 

 termediate characters between the Elasmosauridse and Plesiosau- 

 ridae, the two distinctive families of long-necked plesiosaurs. 

 The two families differ, aside from the skull, especially in the 



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