MUE.ENOSA LTEUS. 77 



Order SAUEOPTERYGIA. 



Carnivorous aquatic reptiles in which the skull has only one temporal arcade and 

 a fixed quadrate ; the pterygoids extending forwards to meet the vomers (1 in all) ; 

 the external nares situated some distance behind the end of the snout ; a pineal 

 foramen present. The teeth are thecodont, and sometimes a few are considerably 

 enlarged ; in tlie later forms they are confined to the edges of the jaws. The tail 

 is relatively short, swimming having been effected mainly by the limbs, which 

 become paddle-like; the hind pair never greatly reduced. Dorsal ribs with a single 

 head ; a plastron of ventral ribs. 



Suborder P L e s i o s a u r i a. 



Clavicular arch undergoing reduction and tending to become situated on the 

 visceral side of a ventral extension of the scapulae, which in the later types replace 

 it functionally ; coracoids large. The ilium is directed backwards and articulates 

 with the ischium only ; the pubis is a broad plate of bone, and the ischia also are 

 generally much expanded. The limbs form oar-like paddles. The plastron consists 

 of a median and several lateral series of overlapping vential ribs. 



Family ELASMOSAURIDiE. 



Head relatively small ; neck long, in some cases excessively so. Cervical ribs with 

 single head. Scapulae meeting in the middle line, where they join the corresponding 

 median anterior prolongations of the coracoids, at least in fully adult individuals. 

 Clavicles and interclavicles may both be present, but one ov both are usually greatly 

 reduced. Epipodial bones much modified, being shortened up so as to resemble 

 mesopodials. 



Middle Jurassic to Cretaceous of Europe, North America, and perhaps New Zealand. 



Genus MURiENOSAURUS, Seeley. 

 [Quart. Journ. Geol. Soc. vol. xxx. (187-1) p. 197.] 



Skull short and broad, of relatively small size. About 24 teeth on each side 

 in the upper jaw, five being situated in the premaxilla ; of the maxillary teeth, the 

 third, fourth, and fifth are enlarged. Mandible with a short symphysis and bearing 



