120 SATJEOPTEEYGIA. 



Family PLESIOSAUBID.E. 



In the skull (when known) the pterygoids diverging posteriorly ; 

 a small infraorbital foramen on either side of the palate 1 . Pectoral 

 vertebrae with a single costal articulation lying partly on the arch 

 and partly on centrum ; dorsals with long transverse processes. 

 Scapulas with large ventral (precoracoidal) plates ; coracoids with 

 very long median symphysis, extending up to or in advance of 

 scapular articulation. Pubis without foramen. Humerus and 

 femur of moderate length and much expanded distally, without 

 foramen or groove ; both these bones (propodials) much larger than 

 epipodials (radius and ulna, and tibula and fibula), which are more 

 or less laterally expanded ; phalangeals increased beyond the normal 

 number, without terminal claws. Limbs probably invested in a 

 common integument, and serving as paddles. 



The humerus and femur may articulate distally with three bones, 

 of which the serial homology is the same as in the Ichthyopterygia 

 {supra, p. 5). 



This family is divided by Seeley 2 into the Pliosauridce, 

 Elasmosauridce, and Plesiosauridce, and if it be considered desirable 

 to split up the genera here adopted some such division would be 

 then necessary. 



Genus PLIOSAURUS, Owen 3 . 



Syn. Ischyrodon, Meyer 4 . 



Spondylosaurus, Fischer 5 . 

 Liopleurodon, Sauvage 6 . 



Skull relatively very large, elongated, with moderately long man- 

 dibular symphysis, which usually extends to the 7th tooth 7 , and 

 the premaxillary and opposing lower teeth enlarged. Teeth large 

 and stout, with strongly marked ridges, and generally a pair of 

 carinas, which are frequently separated by a smooth space. Neck 



1 In the skull of Thaumatosaurus megacephalus figured by Sollas in the 

 ' Quart. Journ. Geol. Soc.' vol. xxxvii. p. 472, fig. 8, the bones marked as 

 palatines (PI.) are really the pterygoids, which reach forward in the usual 

 manner to articulate with the vomer, as in the skull of Plesiosaurus dolichodinis, 

 No. 41101 (infra). 



2 Quart. Journ. Geol. Soc. vol. xxx. pp. 445, 449. 



3 Odontography, pt. ii. p. 282 (1841). 



4 Neues Jahrb. 1838, p. 414. — Description insufficient. 



5 Bull. Soc. Moscou, vol. xviii. pt. i. p. 343 (1845). 



6 Bull. Soc. Geol. France, ser. 3, vol. i. p. 377 (1873). 



7 In the figure of P. brachydirus given by Phillips the postsymphysial portion 

 of the mandible has been crushed together, so as to make the symphysis appear 

 longer. 



