1858.] HUXLEY — PLESIOSAURUS. 287 



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 descriptions 

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

 different from megacephalus, macromus, pachyomus, arcuatus, sub- 

 trigonus, trigonus, brachyspondylus, costatus, doedicomus, rugosus, 

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

 possible to distinguish the detached vertebrse 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 1 2 



Length (oblique longest diameter) 1 5 



Extreme length of head from end of intermaxillary to end of 



quadratum 6 8 



Neck. 



Length of first seventeen cervical vertebrse, measured along their 



bodies 12 9 



Length of following thirteen 15 1 



Giving as entire length of neck 28 



Sixteenth cervical vertebra. 



Centrum. — Longitudinal diameter 9 



Vertical to base of neurapophysis* 1 1 



Thence to top of neural spine 1 4 



Neural spine vertically 8 



Neural spine longitudinally 7 



Costal pit. — Longitudinal measure 5 



Vertical measure 3 



Costal pit to base of neurapophysis 6 



Dorsal region. — Total length 26 5 



Sixth dorsal vertebra. 



Centrum. — Longitudinally 1 25 



Vertically (anterior face) 1 3 



Transversely «. 1 6 



Neural spine. — Vertically 2 1 



Longitudinally 9 



Transverse process. — Length 75 



Antero-posterior diameter 5 



Vertical diameter 75 



Sacral region. — Total length 2\ in. 



* Reckoned as the deepest part of the depression under the zygapophysis, no 

 suture being visible. 



