BIUTISll FOSSIL REPTILES. a/ 



analogy which is indioaled in other animals. The tarsal bones 

 are principally remarkable for their small size on tlie tibial or 

 anterior side of the series, indicating that the hind paddle had 

 a freer inflection forwards, or npon the tibia, than in tlie opposite 

 direction. This structure may have given a compound motion 

 to the propelling stroke of the paddle, similar to that which in 

 skilful rowing is called ' feathering ' the oar. 



The five metatarsals and their digits correspond in structure 

 with those of the fore paddle. The first or tibial metatarsal 

 supports 3 phalanges, the second 5, the third 8 or 9, the fourth 

 8, and the fifth G phalanges. Tlie articular extremities of the 

 phalanges of both the fore and hind paddles are subconcave, 

 with an irregular surface, indicating that they were joined by 

 ligaments or fibro-cartilage, and not by synovial membrane. 



Plesiusaiiriis Haiu/dnsii. 



Having now given a general sketch of the skeleton of the 

 Plesiosaurus, I proceed next to point out the modifications of 

 this type in the different species ; and I shall begin with that 

 of which the greatest number of complete or nearly complete 

 skeletons exist in the British Museum and other collections. 



The species to which these skeletons belong is described and 

 figured in Mr. Hawkins's memoir on IcJithyosauri and Pleslo- 

 saiiri under the name oitriafarsostiims ; 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 

 collection exhibits five tarsal bones on each side,) I propose to 

 describe it under the name of Hawkins's Plesioscnw {Flvsiosau- 

 riis Hawkinsii) as a sincerely offered though inadequate tribute 

 of admiration of the indefatigable labour and rare skill witli which 

 its remains have been disencumbered of their earthy shroud. 



The head of the PL Flawkinsii is of moderate size, smaller 

 in proportion than in the PL maci'ocephahts, and somewhat 

 larger than in the PL dolichodeimis. The neck equals three 

 lengths of the head, and the neck and head together equ;d the 

 trunk and tail. The number of vertebrae throughout the spinal 

 column is between 90 and 100. In the first or anterior 31 

 vertebrae the centrum supports the whole or part of the costal 

 pit : from the 32nd to the 56th vertebra inclusive the costal 

 articular surface is wholly impressed upon the neurapophysis : 

 from the 55th vertebra the costal pit begins again to descend 

 upon the side of the centrum, and it has entirely left the neura- 

 pophysis at the Gist vertebra. At the 80th vertebra the costal 

 processes disappear. 



