734 SLUDGE SHOR SIO DENIS, 
inhabited fresh water. They were powerful swimmers, with 
much better developed limbs than the modern Crocodiles. The 
skin of both the back and abdomen was strengthened by the 
presence of bony plates that formed a very perfect armor. 
Prominent forms were Pelagosaurus from the Upper Lias of Ger- 
many and France; Mystriosaurus, from the same horizon in 
Germany ; Steneosaurus, from the Upper Jurassic of England and 
the continent; Zeleosaurus, from the same horizon and localities, 
etc. Many genera are known from layers younger than the 
Jurassic, and these seem to lead naturally to the Gavialid@, which 
are known from the late Tertiary of India, and are found living 
in the rivers of that country. 
The Srevirostres became prominent in the Upper Jurassic, and 
occupied a very important part in the later times. Of five 
families described two are still living. 
Alligatorellus was a small form from the Upper Jurassic of 
France; it was less than a foot long, 
the possession of biconcave vertebre. 
and was characterized by 
Gontopholis, from the Upper Jurassic of England and the con- 
tinent, was a much larger form than the preceding. It possessed 
biconcave vertebre ; there was a double line of dermal plates in 
the skin of the back, and the ventral surface of the body was 
protected by a large number of plates joined by suture. Similar 
forms have been described by Cope and Marsh, from the Jura of 
the Rocky Mountains, under the names Amphicotylus and Diplo- 
saurus. These may be synonymous with Gonzopholis. 
Lernissartia is from the celebrated fossil region near Bernis- 
sart in Belgium. It is characterized by the fact that the teeth 
are differentiated into separate sizes in the jaws. Theriosuchus, 
from the Purbeck of England, is regarded as belonging to the 
same family. 
The true Alligators and Crocodiles appeared in the fresh 
water deposits of the Cretaceous and extended to the present 
time. Duzplocynodon is one of the earliest of the true Alligators. © 
Remains are found in the deposits of both Europe and North 
America. 
