CLASSIFICATION OF CROCODILIA. 641 
crocodile (C. wzlgarzs) is still formidably common in some of the 
fresh waters of tropical Africa. 
The eggs and the young are often eaten by 2 mammal called the 
Ichneumon, and by a species of lizard. The adults have few enemies 
except man. They seem to live in friendly partnership with little 
birds (Pluvianus egypticus), which remove parasites from the body, and 
in their familiarity almost justify the account which Herodotus gives of 
their cleaning the reptile’s teeth. 
(4) The Alligators, of the genus A//igator, are, with the exception of 
one Chinese species, confined to N. and S. America. In N. America, 
A. mississippiensis, in S. America A. sclerops, is common. 
(c) The Gavials or Gharials, of the genus Gavzalzs, are distinguished 
by their long narrow snout. In the Ganges and its tributaries, G. 
gangeticus, said to attain a length of 20 ft., is common. They feed 
chiefly on fishes. ‘‘ Old males have a large cartilaginous hump on the 
extremity of the snout, containing a small cavity for the retention 
of the air, by which means these individuals are enabled to remain 
under water for a longer time than females or young.” 
DIFFERENCES BETWEEN CROCODILES, ALLIGATORS, 
AND GAVIALS 
ALLIGATORS. CRocoDILEs. GaVIALs. 
The head is short and} Longer. The snout is very long. 
broad. 
First, and fourth lower| The first bites into a| First and fourth iower 
teeth bite into pits in the| pit; the fourth into aj teeth bite into grooves in 
upper jaw. groove. the upper jaw. 
The union of the two; Not beyond the eighth. The union extends at 
rami of the lower jaw does least to the fourteenth. 
not extend beyond the 
fifth tooth. 
The nasal bones form| As in thealligator. The nasal bones do not 
part of the nasal aperture. form part of the nasal 
aperture. 
The teeth are very un-| Unequal. Almost equal. 
equal. 
The scutes on the neck Sometimes distinct, Continuous. 
are distinct from those on | sometimes continuous. 
the back. 
History of Crocodilians.—These giant reptiles form a decadent 
stock. Fossil forms are found in Triassic strata (e.g. Belodon, Para- 
suchus, and Stagonolepis) ; their remains are abundant in Jurassic rocks. 
In Cretaceous strata, crocodilians with proccelous vertebree first occur, 
the pre-Cretaceous forms having centra of the amphiccelous type. 
The oldest crocodilians have the posterior nares situated farther for- 
ward, behind the palatines. Huxley has worked out an “almost 
unbroken” series from the ancient Triassic crocodilians down to those 
of to-day. 
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