C. johnstoni, of Northern Australia and Northern Queensland, and C. intermedius, of the Orinoko, are allied to C. cataphractus, at least so far as the configuration of the bones of the slender and long snout is concerned. The former is small, scarcely reaching the length of 7 feet, while the South American species grows to 13 feet.
C. americanus s. acutus.–This species, which inhabits the West Indian Islands, being there the only representative of the order, occurs also in Florida, and extends through the warmer parts of Central America into Venezuela, Colombia, and Ecuador. Its characteristic feature is a median ridge or swelling on the snout. The length and relative width of the latter varies considerably. The maxillaries sometimes meet dorsally, or they remain separated by the narrow nasals, which in this case reach the posterior corner of the nasal groove. The nuchal scutes vary likewise; there being often a smaller pair on the side of and another behind the four principal scutes, which, as usual, form a square. A transverse row of little suboccipital scutes is also common. Largest size about 12 feet long.
Fig. 111.–Dorsal view of the skull of Crocodilus americanus. × ⅙. F, Frontal; Jg, jugal; L, lacrymal; Mx, maxillary; Na, nasal; P, parietal; Pmx, premaxillary; Prf, prefrontal; Ptf, postfrontal; Qj, quadrato-jugal; Sq, squamosal; T, tooth-perforation.
Osteolaemus tetraspis s. frontatus.–The only species of this genus inhabits the rivers of the west coast of Africa, from Sierra Leone to the Ogowai. It differs from Crocodilus chiefly by the bony septum of the nasal groove, produced by forward extension of the nasal bones. The snout is rather short and stout; the upper surface very rugose and deeply pitted, but without ridges. The gular and ventral scutes are ossified, hence the generic name. Total length about 5 feet.
Alligator.–The fourth mandibular tooth fits into a pit in the upper jaw, and this pit is in some adult specimens transformed into a hole, the tip of the tooth appearing on the upper surface through the perforation. Most of the other teeth of the lower jaw are overlapped by those of the upper jaw. The number of teeth on either side amounts to seventeen to twenty in the upper and eighteen to twenty in the lower jaw. The nasal bones form not only the posterior border of the nasal groove, but they divide the latter by a median bony septum. The dorsal shield is formed by six or eight longitudinal series of keeled bony scutes, which, although standing close together, do not articulate with each other. Ossification of the gular and ventral scutes is absent or very slight.
Alligators occur in the fluviatile deposits of the age of the Upper Chalk in Europe, where they did not die out until the Pliocene age; they are now restricted to two species, one in the Southern States of North America, the other in China.
A. mississippiensis.–The much-depressed and broadly rounded snout bears some resemblance to that of a pike, hence the now discarded specific name of lucius. The neck is protected by two pairs of large scutes, which form a square, interrupted in the middle line, with a pair of small scutes in front and another behind. Of the eighteen transverse dorsal rows of scutes eight are broad and prominent. The fingers are about half webbed, the outer toes about two-thirds webbed. The general colour is greenish black or dark brown above, yellowish below. Young specimens have yellowish cross-bands on a darker brown ground.
The Alligator's northern limit is the mouth of the river Neuss in North Carolina, 35° N. lat. From this point they abound near the mouths of all the creeks and rivers as far south as the Rio Grande, ascending the Mississippi to the entrance of the Red River in 33° 50' N. lat.
The habits and the embryology of the American Alligator have been described by S. F. Clarke,[[143]] who gives the following vivid and minute account:–