VIII. AN UNDETERMINED ELEMENT IN THE OSTE- 

 OLOGY OF THE MOSASAURID^:. 



By W. J. Holland. 



In the collection of Baron Ernest Bayet, purchased in 1903 by Mr. 

 Andrew Carnegie for the Museum of the Institute in Pittsburgh, was a 

 skeleton of Mosasanrus lemonnieri Dollo, discovered at Cuesmes, Bel- 

 gium. It is mounted free, and though lacking the phalanges of the 

 paddles, is otherwise one of the best specimens representing the genus 

 and species in existence. Associated with the skeleton was a bone 

 which had evidently been identified as a portion of the sternum, for it 

 was placed on the floor of the case in which the skeleton was displayed 

 in such a position as to indicate that the preparator supposed that it 

 might be properly assigned to the sternum. Dr. A. Smith Woodward, 

 who reported upon the Bayet Collection to the Trustees of the British 

 Museum with a view to its purchase, and who kindly allowed me to 

 make a copy of his report preserved in the files of the National Mu- 

 seum in London, in speaking of the skeleton of Mosasaurus says that 

 it includes a " sternum ? " The reference of the bone to the sternum 

 was evidently a matter of doubt in the mind of Dr. Woodward. Last 

 summer, when freeing from the matrix and mounting the bones of a 

 fine specimen of Clidastes tortor Cope, now displayed as a slab mount 

 in the Carnegie Museum, a portion of a similar bone was found asso- 

 ciated with the remains and lying very near the lower margin of the 

 inferior maxillary bones. In the summer of 1906 I called the atten- 

 tion of Dr. S. W. Williston, who was visiting me, and who has de- 

 voted more time and attention to the osteology of the Mosasauridse 

 than any other American student, to the bone belonging to the spec- 

 imen found at Cuesmes. I suggested to him that the bone might be 

 possibly regarded as a glossohyal bone, or that it might be the xiphis- 

 ternum, stating that I was inclined to prefer the first hypothesis. At 

 that time the specimen found associated with the remains of Clidastes 

 tortor had not turned up. Subsequently, having found the latter 

 specimen, I wrote to Dr. Williston, enclosing sketches of both bones, 

 and asking him to again give me the benefit of his great knowledge of 



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