172 REPORT OF NATIONAL MUSEUM, 1898. 



Ooncerniug this geuus Bouleiiger remarks : ' 



Notwithstanding all that has heen written on the specific characters of the croco- 

 diles, their distinction and definition remains a matter of considerable difficulty. 

 Although the extreni(3 forms, viz, C. cataphractiis and C.palustris, differ very widely, 

 the passage is so comi)lcte as to render even subgeneric divisions unadvisable. The 

 following key will. I hope, suffice in most cases for the exact determination of the, 

 species, except with respect to newly born specimens, which can only be named by 

 comparison with older examples. 



Bouleager then gives the following table of the species : 



f. Snout very slender, gavial-like, at least twice as long as broad at the base; man- 

 dibular symphysis extending to the level of the sixth, seventh, or 

 eighth tooth; premaxillo-maxillary suture, on the palate, prodiiced 

 posteriorly. 



Nuchal scutes in two longitudinal series, continuous or subcontiuuous 

 with the dorsals C. cataphractus Cuvier. 



Nuchal scutes six, four in a square with one on each side, subcoutinuous 

 with the dorsals C. johnstonii Krefl't. 



Nuchal scutes six, four in a square with one on each side, widely sepa- 

 rated from the dorsals C. intermedins Graves. 



II. Snout more than once and a half, and not more than twice and a one-fourth as 



long as broad at the base; mandibular symphysis extending to the 

 level of the fourth or fifth tooth; premaxillo-maxillary suture, on the 

 jialate, produced posteriorly. 



A. No longitudinal ridge in front of the eye; anterior nuchal scutes (post- 



occipitals) well developed. 

 A longitudinal swelling or ridge along the middle of the snout. 



C. americanus Laurenti. 

 A longitudinal ridge between the orbits, none on the snout. 



C. siamensis Schneider. 

 No ridges on the forehead or snout C. niloticus Laurenti. 



B. A longitudinal ridge iu front of the eye; anterior nuchals usually absent. 



C. porosus Schneider. 



III. Snout not more than once and a half as long as broad at the base; mandibular 



symphysis extending to the level of the fourth or fifth tooth, premaxillo- 

 maxillary suture, on the palate, transverse or curved forward. 



A. Snout without ridges. 



Dorsal shield usually composed of four longitudinal series of scutes, the 



median of which are broader than long. C. palustris Lesson. 



Dorsal shield composed of six longitudinal series of scutes in the mid- 

 -» die C. rohmitns Vaillant and Grandidier. 



B. A more or less distinct oblique ridge in front of the eye. 



Scales on upper surface of limbs keeled C. rhomhifer Cuvier, 



Scales on limbs perfectly smooth C. moreletn A. Dum6rii. 



Species of this genus are abundant in the Cenozoic formations from 

 tlie Eocene onward, but they become rarer in the later beds. The 

 above-mentioned existing species are distributed as follows: 



Neotropica. Ethiopica. Indica. 



G. americanus. G. cataphractus. G. siamensis. 



G. intermedius. G. niloticus. G. porosus. 



G. rhomhifer . G. robustus. G. palustris. 



G. moreletn. 



/ Australasica. 



G. johnstonii. 



' Cat. Cheloniaus, Rhynchocephalians, and Crocodiles, Hrit. Mus., London, 1889, 

 p. 277. 



