604 REPTILIA [CU. 



termed the Dicynodontia are believed by some to have been the 

 forerunners of the Chelonia. 



A third group of Monapsida was constituted by the great group 

 of whale-like Reptiles known as Ichthyosauria in which the neck was 

 absent and the limbs were transformed into flippers the fingers 

 being represented by long rows of squarish bones. The fingers 

 frequently branched and supernumerary fingers were formed. Some 

 exceptionally well preserved specimens show that the animals when 

 alive possessed a dorsal fin. 



The other division of the Cotylosaurian stem consisted of forms 

 in which supratemporal and laterotemporal fossae were equally de- 

 veloped ; these were the Diapsid Reptiles. The Rhynchocephala as 

 represented by Sphenodon are almost unmodified survivors of the 

 early Diapsida. From this group in the following age were developed 

 (a) Water-Reptiles the Plesiosauria with long swan -like necks 

 and limbs transformed into flippers by the shortening of the bones 

 of the arm and leg, and (6) Land-Reptiles the Dinosauria with 

 greatly developed limbs ; in some cases the whole weight was 

 borne by the hind-limbs, the fore-limbs being short and used for 

 prehensile purposes only. In a still later period from the less 

 specialised Dinosauria were developed (l) the Crocodilia, which 

 reverted to the water but retained limbs fit for progression, and 

 (2) Pterosauria, flying reptiles in which the "wing" was a flap of 

 skin supported by the greatly elongated 5th finger. The forerunners 

 of modern Sauria are found only in the Chalk period in the form 

 of long-bodied aquatic Reptiles showing the characteristic loss of 

 the quadratojugal. 



The class Reptilia is classified as follows : 



Order I. Rhynchocephala. 



Reptilia devoid of special copulatory organs arid with an 

 immovable quadrate. 

 Ex. Sphenodon. 



Order II. Sauria. 



Reptilia with paired dorsal copulatory organs and a 

 movable quadrate. 

 Sub-order 1. Lacertilia. 



Sauria which retain a pectoral girdle and a urinary 

 bladder ; in which the rami of the lower jaw are united by a 

 symphysis. Limbs present or absent. 



Ex. Lacerta, Anguis. 





