I PROF. HUXLEY ON TKE SPECIFIC AND GENERIC 



reach ; and I therefore propose to preface my account of the pecu- 

 liarities of the exoskeleton in two of the genera of recent Croco- 

 diles with some remarks on the classification of the group, and 

 with a few notes upon the characters of the species and the limits 

 of the genera. 



Everyone is acquainted with the great improvement effected in 

 this branch of Herpetology by Cuvier, who divided the Crocodiles, 

 which he regarded as constituting only a single genus, into the 

 three subgenera Alligatores, Crocodili, and Longirostres. Subse- 

 quent writers have admitted these highly natural subdivisions ; 

 but there has been a constant tendency to raise their rank. The 

 genus Crocodiltis has become the order Croeodilia ; the subgenera 

 Alligatores, &e., have been elevated into families ; Dr. G-ray has 

 shown that the Alligatores must be divided into three genera, and 

 that there are at least two genera of Crocodili ; and, while one of 

 Cuvier's species of Longirostres has been suppressed, the group 

 is very generally retained with a changed name {Gavialis), sl 

 very important addition having been made to it in the Crocodilus 

 Schlegelii of Miiller and Schlegel. 



Unless the considerable materials contained in the British 

 Museum, the Hunterian collection, the collection of Dr. Grant, 

 and the Christchurch Museum at Oxford had been freely placed 

 at my disposal, I should have been wholly unable to acquire the 

 information contained in the following pages. It is only right, 

 therefore, that I should take this opportunity of offering my 

 thanks to my friends Dr. Gray, Prof. Quekett, Dr. Grant, and 

 Dr. B-oUeston for the many facilities they have liberally afibrded 

 me. 



The recent species of the order Croeodilia are divisible into 

 three families, which correspond with the original subgenera of 

 Cuvier, and may be termed the Alligatoridcd, the CrocodilidcB, and 

 the GavialidcB. 



I. In the Alligatoridje the teeth are strong and unequal, and 

 the posterior ones differ greatly in shape from the anterior. The 

 anterior pair of mandibular teeth, and the fourth pair (or the so- 

 called canines) are receivedinto pits in the margins of the premaxilla 

 and maxilla ; while the mandibular teeth behind these pass inside, 

 and not between, the maxillary teeth. The mandibular symphysis 

 does not extend back beyond the level of the fifth tooth, and often 

 not nearly so far. The line of the premaxillo-maxillary suture on 

 the palate is straight, or convex forwards. The wide posterior 

 nares look downwards, and are situated forwards on the palate. 



