FOSSIL VERTEBRATES — REPTILIA 719 
snakes, allowing a very great freedom of movement to the body. 
The limbs were modified as swimming organs. As in the case of 
land forms generally which have become adapted to an aquatic 
life, the number of the phalanges was increased, while the 
shape of these and of the tarsal and the carpal bones became 
indefinite, and, in some cases, they were even reduced to mere 
flattened disks of bone. 
The geographical range of the Pythonomorpha is rather remark- 
able. They are known from the Upper Cretaceous rocks only, 
ranging from the Upper Dakota to the Lower Laramie. They 
have been found in the rocks of the western part of the United 
States, in Kansas and the Dakotas and in the Cretaceous deposits 
of New Jersey and Alabama; in the Maestricht beds, Lower Danian, 
of Belgium; inthe Upper Cretaceous of England, the Chalkbeds, 
which are supposed to be correlated in time with the Niobrara 
beds of western Kansas; in Upper Cretaceous beds of unknown 
position on the coast of Chile and upon some of the adjacent 
islands, and in the same horizon in New Zealand. 
The order is divided into three groups: the subfamilies 
Tylosaurine, Platecarpine, and Mosasaurine. Below is an abbrevi- 
ated list of the characters assigned by Williston to the various 
divisions. 
Tylosaurine.: hind feet functionally pentadactyl; trunk short, 
tail proportionately long; tarsus and carpus almost wholly 
unossified, phalanges numerous; premaxillaries projecting as a 
long rostrum in front of the teeth. 
Tylosaurus.—This is one of the largest of the forms. It 
reached in some cases, 7. dyspelor,a length of nearly 30 feet. 
There were 7 cervicals, 29-30 precaudals, 80 caudals. From the 
Upper Cretaceous of New Zealand, Kansas, New Mexico, and 
New Jersey. 
Flammosaurus: less well known; from the Upper Senonian of 
Cipley* (Brown Phosphate Chalk) in France. 
Platecarpine: hind feet functionally pentadactyl; trunk short, 
tail proportionately long ; carpal and tarsal bones not well ossi- 
fied; premaxillaries, not projecting in front of the teeth, obtuse. 
