I have not been able to obtain any skull of this species, which, according to Cuvier's account and figures ('Oss. Fossiles,' t. ix. p. 102), resembles C. Americanus in the great convexity of its nasal region, but differs from it in the greater breadth of the skull, and in the strong converging preorbital ridges, which appear to be limited to the lachrymal bones. If the figures are to be I trusted, however, there are other very important distinctive characters about the cranium of this species; for Cuvier's, fig. 2, pl. 331, which gives a view of the palate, shows the premaxillo-maxillary suture forming a nearly straight transverse line.
There remain several species of Crocodilus whose skulls I have not been able to examine, and of which no sufficient descriptions exist. Of these, (7.) C. galeatus and (8.) C. Gravesii (planirostris) would appear to be very distinct forms. (9.) C. marginatus is considered by Duméril and Bibron to be only a variety of C. vulgaris; and they take the same view of (10.) Crocodilus suchus. Professor Owen, however, has figured the cranium of an Egyptian mummy under this name ('Monograph on the Reptilia of the London Clay,' Pal. Soc., 1850). In the under-view of this skull (tab. i. fig. 2), the junction of the premaxilla and the maxilla in the palate seems to be broken away; but on the left side, the palatine process of the maxilla is entire, as far as the level of the anterior margin of the sixth tooth, and there is not a trace of a suture behind this point. Are there, then, two or more species of Crocodile in Egypt, as Geoffroy St.-Hilaire supposed?
With regard to the distribution of the species of Crocodilus, C. vulgaris, C. marginatus, and C. suchus(?) appear to be exclusively African; all the crocodiles from other parts of the Eastern hemisphere, which I have met with, belong, as I have stated above, either to C. biporcatus or C. bombifrons, both of which species are found in the Ganges. Crocodilus galeatus appears to be peculiar to Siam. Crocodilus Americanus and C. rhombifer are undoubtedly American. C. Journei has been supposed to be African; but such positive evidence as exists tends rather to prove it to be an American species. Thus Bory de St. Vincent states that the Bordeaux specimen is "suspected to have come from America;" and, as I have said, the skull in the British Museum is labelled "from the Orinoko."
Crocodilus Gravesii (planirostris) is supposed by Bory de St. Vincent to have been brought from the Congo; but its real origin is not known.
Genus 5. Mecistops.
The cranium is elongated, and the snout slender and Gavial-like. There are eighteen slender and subequal teeth above, and fifteen below, on each side. The mandibular symphysis extends back to the level of the seventh tooth. The cervical scutes are arranged in two transverse rows, each of which contains two scutes; and there is no space left between the posterior row and the tergal series.
This excellent genus, as established by Dr. Gray, includes Cuvier's Crocodilus cataphractus (which Dr. Gray considers to be the young of a species whose full-grown form was discovered by Mr. Bennett in West Africa), Crocodilus Journei and Crocodilus Schlegelii. As I have endeavoured to show, however, C. Journei is a true crocodile; and, as I shall point out below, Müller and Schlegel have satisfactorily proved C. Schlegelii to be a Gavial. Consequently Mecistops is at present represented by only one species, which must be called M. cataphractus if M. Bennettii of Gray is really the adult of the form which Cuvier described.
III. In the family of the Gavialidæ, the snout is always very long and slender; the teeth are for the most part slender, sharp-edged, and subequal. The two anterior mandibular teeth pass into grooves, one of which lies on each side of a beak-like prominence of the premaxillæ, which carries the two anterior upper teeth. The canines are received into grooves. The mandibular symphysis extends back to at least the fourteenth tooth, and is partly formed by the junction of the splenial bones. The premaxillo-maxillary suture is always strongly convex backwards. The posterior nares are situated more forward than in the Crocodili. The temporal fossæ are large. The feet are strongly webbed. The dorsal scutes are not articulated; and there are no ventral scutes.