SAUROPTERYGIA. 37 1 



tebrae were either flat or only slightly cupped at each end, and 

 the neural arches were anchylosed with the centra, and did 

 not remain distinct during life. The transverse processes of 

 the vertebrae were long, and the anterior trunk-ribs had simple, 

 not bifurcate, heads. No sternum or sternal ribs are known 

 to have existed, but there were false abdominal ribs. The 

 neck, in most, was greatly elongated, and composed of numer- 

 ous vertebras. The sacrum was composed of two vertebrae. 

 The orbits were of large size, and there was a long snout, as 

 in the Ichthyosauri, but there was no circle of bony plates in 

 the sclerotic. The limbs agree with those of the Ichthyosauri 

 in being in the form of swimming-paddles (fig. 321), but differ 

 in not possessing any supernumerary marginal ossicles. A 

 pectoral arch, formed of two clavicles and an interclavicle 

 (episternum), appears to have been sometimes, if not always, 

 present. The teeth were simple, and were inserted into dis- 

 tinct sockets, and not lodged in a common groove. 



Fig. 321. Plesiosaurus dolichodeirus. Lias. 



The most familiar and typical member of the Sauropterygia 

 is the Plesiosaurus (fig. 321), a gigantic marine reptile > chiefly 

 characteristic of the Lias and Oolites. As regards the habits 

 of the Plesiosaurus, Dr Conybeare arrives at the following con- 

 clusions : " That it was aquatic is evident from the form of 

 its paddles ; that it was marine is almost equally so from the 

 remains with which it is universally associated ; that it may 

 have occasionally visited the shore, the resemblance of its ex- 

 tremities to those of the Turtles may lead us to conjecture ; 

 its movements, however, must have been very awkward on 

 land ; and its long neck must have impeded its progress 



