1858.] HUXLEY — PLESIOSAURUS. 281 



2. On a New Species of Plesiosaurus from Street, near Glas- 

 tonbury ; with Remarks on the Structure of the Atlas and 

 Axis Vertebrae, and of the Cranium, in that Genus. Bv 

 Thomas H. Huxley, F.R.S., F.G.S., Professor of Nat. Hist. &c. 



The locality where the Plesiosaurus, which forms the subject of the 

 present brief notice*, was obtained is already famous for its richness 

 in such remains. In fact, the limestone beds of the Lower Lias at 

 Street have already yielded at least three species of Plesiosaurus — 

 P. Hawkinsii, P. macrocephalus, and P. megacephalus ; and it seemed 

 so unlikely that a fourth species should have inhabited the same 

 area, that I was for a long while unwilling" to admit the distinctness 

 of the form at present under consideration. 



The evidence which I shall bring forward, however, seems to me 

 to admit of no other conclusion. 



The specimen is a remarkably fine one. The limestone matrix in 

 which it is imbedded being hard and free from pyrites, every part is 

 well preserved ; and the value of the fossil is further enhanced by 

 two circumstances : — first, the very slight amount of disturbance 

 which the bones have undergone, so that the vertebrae from the third 

 cervical to the last caudal are all in their natural positions ; secondly, 

 the perfectly lateral view of the body which is presented. The only 

 important defects are the absence of the paddles, and the flattening 

 and apparent loss of the lower jaw which the head has suffered . 



The total length of the skeleton is about 7\ feet. The left side 

 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 Plesiosaurus, I think I cannot do better 

 than name it after him, P. Etheridgii. 



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 f) is less than one- thirteenth of 

 the whole length of the body. As the anterior teeth have nearly 

 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 premaxillaries clearly shows that the allowance to be made on 

 this ground, if any, must be very small. 



* The specimen will be fully described and figured in the Decades of the Geo- 

 logical Survey of Great Britain. 



t The " length of the head" measured from the end of the snout to the poste- 

 rior 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. 



