ON A NEW SPECIES OF PLESIOSAURUS 529 



and, though its produced angle is more or less broken, its hatchet- 

 shape can be clearly distinguished. The costal articular facets of 

 both the 30th and 31st vertebrae are traversed by the neurapophysial 

 suture. 



In No. 2 the condition of the posterior cervical vertebrae is such as 

 to render it very unsafe to speak decidedly as to the character of either 

 the ribs or their articular facets. 



So far as these specimens go, then, they favour the idea that P 

 Hawkinsii has 3 1 vertebrae cervical in Prof Owen's sense of the term, 

 and they assuredly do not countenance the notion that these vertebrae 

 ma}' vary in the same species. But if Plesiosaiirus Hazvkinsii has 54 

 or 56 cervico-dorsal vetebrse, and if 3 1 of these are cervical, then P. 

 Etheridgii differs from it in the following particulars : — 



1. The number of cervical vertebrae is at least one less. 



2. The number of cervico-dorsal vertebrae is one or three less. 



3. The head is shorter in proportion to the body. 



4. The head is shorter in proportion to the neck. 



I think then there can be no doubt as to the specific distinctness 

 of P. Etheridgii from all the Plesiosauri as yet mentioned. 



With regard to the other species, I judge from the description.? 

 and from such specimens as I have seen, that P Etheridgii is very 

 different from niegacephalus, macroinus, pachyonius, arcuatus, siib- 

 trigonus, trigonus, brachyspondybis, costatus, dcedicoinus, rngosus, 

 trochanteriiis, and affinis. I doubt at present whether it would be 

 possible to distinguish the detached vertebras of P Etheridgii from 

 those of P. Hawkinsii ; but I believe, having examined the series of 

 vertebrae in the College of Surgeons' Museum, on which some four- 

 teen species have been founded, they are all different from those of 

 P. Etheridgii. 



The measurements of the different parts are as follows, in inches, 

 and tenths : — 



Head. 



in. tenths.. 

 From end of intermaxillary to end of occipital condyle 6 5 



End of intermaxillary to anterior margin of orbit 2 15 



End of intermaxillary to anterior end of parietal foramen 4 2 



Width of orbit I 2 



Length (oblique longest diameter) i 5 



Extreme length of head from end of intermaxillary to end of quadratum 6 8 



Neck. 



Length of first seventeen cervical vertebrae, measured along their bodies 12 9 



Length of following thirteen 15 i 



Giving as entire length of neck 28 o 



M JNI 



