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. I distinguish two genera in this family, _Rhynchosuchus_ and _Gavialis_. Genus 6. RHYNCHOSUCHUS.