ON A NEW SPECIES OF PLESIOSAURUS 523; 



is exposed, and the neck and tail are strongly bent upwards, as if the 

 creature had died in a state of opisthotonic rigidity. The head is 

 twisted, so that its upper surface only is visible, and it is at the same 

 time bent back, at right angles to the neck. In consequence of this,, 

 the occipital condyle and the atlas are well separated. The two 

 anterior cervical vertebrae were originally partially covered by the 

 crushed right os quadratum ; but by removing the latter both atlas 

 and axis have been very clearly exposed. 



As the Museum of Practical Geology is indebted to the judgment 

 and energy of my friend and colleague Mr. Robert Etheridge, F.G.S.,. 

 for the acquisition of this fine Pksiosaurus, I think I cannot do better 

 than name it after him, P. Etiieridgii. 



The following are the most important characters of this species : — 



1. The length of the skull (measured from the end of the pre- 

 maxillaries to the occipital condyle i) is less than one-thirteenth of 

 the whole length of the body. As the anterior teeth have nearl)- 

 disappeared, it is not certain that the skull may not have borne a 

 slightly larger proportion to the body ; but the anterior slope of the 

 prema.xillaries clearly shows that the allowance to be made on this 

 ground, if any, must be very small. 



2. There are thirty cervical vertebrje — vertebrae, that is, which 

 present facets for articulation with ribs on the lower half of their 

 centrum ; the ribs being short and compressed superiorly, or hatchet- 

 shaped."^ 



3. Three times the length of the skull equals the length of the 

 anterior twenty-three cervical vertebrae ; four times the same length 

 equals the anterior twenty -eight cervical vertebrte. It follows therefore 

 that the neck is between four and five times as long as the skull. 



4. There are about 90 vertebrae, of which 30 are cervical, 23 dorsal, 

 2 sacral, and 34 or 35 caudal. 



5. The humerus and the femur are as nearly as may be equal in 

 size. 



6. The vertical diameter of the centra of the anterior cervical ver- 

 tebrse is greater than the longitudinal, the proportion being at least as 

 three to two in the third cervical. In the thirtieth cervical the two 



' The "length of the head" measured from the end of the snout to the posterior 

 extremity of the lower jaw is commonly taken as the unit of comparison. But the end of the 

 OS quadratum and the lower jaw are so readily displaced as to render this anything but a safe 

 standard. 



^ The neurapophysial sutures are not visible ; but as there is reason to believe that the 

 neurapophyses do not extend upon the bodies of the cervical vertebrse beyond their dorsal 

 half, the character of a cervical vertebra here used is probably equivalent to that employed by 

 Prof. Owen {loc. cil. ). 



