478 PLESIOSAURIA CHAP. 



nearly 5 feet long and 2 feet broad, armed with many enor- 

 mous conical teeth, some of which reach one foot in length, 

 inclusive of the long collar and root -portion. The neck is 

 rather short, owing to the much condensed, disc-shaped centra 

 of the vertebrae. Total length of this species about 30 feet. 

 Other species in England and continental Europe as far as Russia. 



Fam. 2. Plesiosauridae. The neck is very long, and consists 

 of from twenty -eight to forty vertebrae. The scapulae do not meet 

 ventrally, but the symphysial portion of the coracoids meets the 

 clavicles and the interclavicle, the pectoral arch thus enclosing 

 two foramina. Chief genus Plesiosaurus, with many species. The 

 head is comparatively small, the neck very long, the tail short, 

 although consisting of from thirty to forty vertebrae. The third 

 digit (Fig. 113,0) is the longest,and possesses nineor ten phalanges. 

 The abdominal ribs are very strong, and reach from the pectoral to 

 the pelvic girdle. Range from the Lower Trias to the Lower 

 Oolite, chiefly European. P. dolichodirus and P. conybeari, the 

 latter reaching a total length of more than 15 feet, from the 

 Lower Lias, especially at Lyme Regis. 



Fam. 3. Elasmosauridae. The neck is extremely long, posses- 

 sing from thirty-five to seventy-two vertebrae, with single-headed, 

 not bifurcated, ribs. The scapulae meet ventrally, and enclose with 

 the very broad coracoids two foramina. The tail is short. The 

 pisiform bone articulates with the humerus. Otherwise much re- 

 sembling the Plesiosauridae. Principal genus Cimoliasaurus, with 

 many synonyms, and many species from the Middle Oolite to the 

 Upper Chalk ; cosmopolitan distribution, e.g. C. cantabrigiensis, of 

 the Greensand and Upper Chalk : C. trochantericus, of the Kim- 

 meridge clay ; C. haasti in New Zealand ; C. australis, C. chilensis ; 

 others in North America. Cryptoclidus of the Middle and Upper 

 Oolite of Europe. Elasmosaurus, of the Upper Cretaceous forma- 

 tion in Kansas, with a computed total length of 45 feet, of which 

 22 belong to the neck, with its seventy-two vertebrae. 



SUB-CLASS VIII.ICHTHYOSA URIA. 



Marine, whale- shaped reptiles, with the anterior and posterior 

 limbs transformed into hyperphalangeal paddles. Restricted 

 to the Mesozoic age from the Trias to the Upper Chalk. 



The skull is long, owing to the elongated slender snout, which 



