CHAEACTEES OF RECENT CEOCODILIA. S 



This family embraces three genera, readily distinguishable by 

 osteological characters — Alligator, Caiman, and Jacare. 



Genus 1. Alligator. 



Dental formula, ^^Ei^. 9th maxillary tooth the largest of its 

 series. The snout is very broad, flattened, and rounded at the 

 end. There is an indistinct longitudinal interorbital ridge ; and 

 there are two short ridges along the line of junction of the pre- 

 frontal and lachrymal bones. The aperture of the external nares 

 is divided into two parts, by the prolongation forwards of the nasal 

 bones. The supra-temporal fossae are well-marked and open, though 

 not large. The vomers do not appear in the palate. The feet 

 are well webbed. The dorsal bony scutes are not articulated 

 together ; and there are no ventral scutes. 



This genus contains only one species, the well-known Alligator 

 3Iississipiensis, or lucius, which is exclusively North American. 



Cuvier (Oss. Foss. ed. 4. vol. ix. p. 211) gives the appearance 

 of the vomer in the palate as a general character of the Alligator es ; 

 but this bone is not visible in the palate of any of those Alligatores 

 which Cuvier would have referred to his A. lucius or A.palpehrosus, 

 and which form the genera Alligator and Cahnan as here defined. 

 The vomers are in fact as slender and delicate as in the Crocodile, 

 and extend only between the level of the tenth maxillary tooth an- 

 teriorly and the descending processes of the prefrontal posteriorly. 



What may be called the median nares, or the arch formed by 

 the postero-lateral part of the vomer and the anterior and superior 

 lamina of the palatine bone on each side (which would constitute 

 the posterior boundary of the posterior nares, if the palatine and 

 pterygoid bones gave off no inferior or palatine processes), are 

 situated nearly on a level with the twelfth tooth, or with the 

 palato-maxillary suture. 



Genus 2. Caiman. 



Dental formida ^^^ (Natterer). The face is without median 



or transverse ridges, but it is sharply angulated along a line which 

 extends from the orbit forwards along the sides of the snout. The 

 anterior nasal aperture is undivided in the dry skull. The vomers 

 do not appear in the palate. The supra-temporal fossae are obli- 

 terated, the circumjacent bones uniting over them. The webs of 

 the feet are rudimentary. The dorsal scutes are articulated to- 

 gether by lateral sutures and anterior and posterior facets ; and 

 there is a ventral shield, consisting of similarly articulated scutes. 



1* 



