REPTILES. 647 
orbit; parietal foramen none; alisphenoids large; orbitosphenoid rudimentary or 
wanting; vertebre completely ossified, procelous except atlas, dentatus, the two 
gacrals and first caudal; in extinct species amphi- or opisthocelous; cervical vertebrae 
with small ribs; ribs articulating with the vertebra by means of a head and tubercle ; 
always oviparous. 
Inhabit fresh water in hot countries. 
The Crocodilians are all extra-limital. The existing forms may be divided as 
fellows: 
Muzzle large and flat. a. 
Muzzle elongated, rounded and dilated at the end. : : 4 GAVIALIDZ:. 
a. Fourth tooth in lower jaw received into a notch on the side of the upper 
maxillary ; hind legs with a toothed fringe, and toes completely palmated. 
CROCODILIDA. 
a. Fourth or canine tooth in lower jaw received into a fossa in the upper; hind 
legs simply rounded and toes semipalmate. : ‘ . ALLIGATORIDA. 
Gavialide, the Gavials, comprise two genera, Gavialis, one species, G. gangeticus, in- 
habiting the Ganges, and Somistoma, two species, in the rivers of Borneo and 
North Australia. 
Crocodilide, the Crocodiles, has one genus, Crocodilus, with four American, three 
African, four Asiatic, and one Australian species. On this continent they are not found 
north of Yucatan, Guatemala, or Cuba, except one species, Crocodilus americanus, which 
occurs in Florida. 
Alligatoridz, the Alligators or Caimans, comprise also but a single genus, Alligator, 
with ten species, and are iimited to the New World. 
Alligator mississippiensis or lucius is the common Alligator of our Southern States. It 
is dark ash-brown above, paler beneath; dorsal plates with elevations forming discon- 
nected lor gitudinal ridges ; four of these carinate plates upon the neck are arranged qaad- 
rately. 
