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XXXVII. —^ Description of a Specimen of the Plesiosaurus Macro- 

 CEPHALUS, Conybeare, in the Collection of Viscount Cole, M.P., 

 D.C.L., F.G.S., &c. 



By RICHARD OWEN, Esq., F.R.S., F.G.S., Hunterian Professor to the 

 Royal College of Surgeons, London. 



Plates XLIIL, XLIV., XLV. 



[Read April 4th, 1838.] 



Lord cole having done me the honour to transmit to me for description, 

 his unique specimen of the Plesiosaurus macrocephalus, I have endeavoured 

 to devote to it an examination equivalent in care and detail to the admirable 

 completeness of many of its parts, and have reason to hope that it will throw 

 additional light on the Plesiosaurian modifications of the vertebrate skeleton^ as 

 well as on some interesting points in general osteology. The study of the 

 spinal column has induced me to reconsider the views generally adopted as to 

 the composition of a vertebra ; and I have found it convenient, if not abso- 

 lutely requisite, to give new names, applicable both in the abstract and con- 

 crete senses, to some of the component vertebral elements. The chief specific 

 characters are also premised of another Plesiosaur, which, from the complete- 

 ness of its skeletons in our national and other collections, it seemed most advan- 

 tageous to adopt as a term of comparison with the present specimen. 



The species to which I refer, is that which is described and figured in Mr. 

 Hawkins's" memoir on Ichthyosauri and Plesiosauri *, under the name of Tria- 

 tarsostinus ; but as this designation relates to an imperfect state of the tarsus 

 in the right foot, (for a fourth bone is present in the left tarsus of the same 

 specimen, and a second specimen of the same species in Mr. Hawkins's col- 

 lection exhibits five tarsal bones on each side,) I propose to refer to it under 

 the name of Hawkins's Plesiosaur {Plesiosaurus Hawkinsii), as a well- 

 deserved tribute to the indefatigable labour and remarkable skill to which 

 we are indebted for our knowledge of this interesting species. To subse- 

 quent figures, as well as to the casts of this beautiful fossil, has been applied 

 the name of PL Dolichodeirus, which was originally given by Mr. Cony- 

 beare to the Plesiosaur in the collection of His Grace the Duke of Buck- 



* Plate XXIV, 

 VOL. V. SECOND SERIES. 3 X 



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