50 Mr. H. Seeley on Plesiosaurus macropterus, 



1. P. Cramptoni, Baily & Carte. 

 Head one-sixth of skeleton and five- eighths of neck. Vertebra? : 

 27 cervical, 30 dorsal, caudal 34+ . Length 22 feet 5 inches. 



2. P. macrocephalus, Ow. 



Neck equal to two heads. Vertebrae : 29 cervical, 20 dorsal, 

 2 sacral. 



3. P. brachycephalus, Ow. 



Head one-eighth of skeleton. Vertebrae 75 : 28 cervical. Length 

 101 feet. 



4. P. Hawkinsi, Ow. 



Head one-tenth of skeleton. Neck equal to four heads. Tail 

 equal to two and a half heads. Vertebra? 90 to 100 : 31 cer- 

 vical, 23 dorsal, 2 sacral, 35 caudal. Length 7^ feet. 



5. P. Etheridgii, Huxley. 



Head one-twelfth of skeleton. Four lengths of skull equal 

 to anterior 28 cervical vertebra?. Vertebra? 90 : 30 cervical, 

 23 dorsal. Length 7\ feet. 



6. P. dolichodeirus, Conbr. 



Head one-thirteenth. Neck equal to four lengths of head. Ver- 

 tebra? : 35 cervical, 27 dorsal, 2 sacral, 26 caudal. Length 

 10 feet. 



But if our species is compared with these, it ranges itself at 

 the opposite end of the series to P. Cramptoni, having relatively 

 the longest neck and smallest head, as may be here shown. 



7. P. macropterus. 



Head one-twentieth of skeleton, and one-eighth of the neck. 

 Vertebra? : cervical 39, dorsal 24, caudal 28. Length 15 feet 

 2 inches. 



I have also satisfied myself that our species is quite distinct 

 from those which have been made from a few bones. 



The orbits, nares, &c. are not to be distinguished ; for the 

 skull has been compressed : it is oblong, tapering in a parabola 

 to the front. The teeth are slender, finely striated, curved, and 

 an inch long : they appear to be most numerous in the anterior 

 part of the jaw. The total length of the skull is 9 inches. 

 From the parietal crest to the tip of the premaxillaries is 6 inches. 

 The width of the skull is 4^ inches. 



The rami of the lower jaw are massive, 9| inches long, and 

 \\ inch deep, and are united by symphysis at their anterior 



