ON THE DERMAL ARMOUR OF JACARE AND CAIMAN 287 
which he regarded as constituting only a single genus, into the three 
subgenera Adligatores, Crocodili, and Longirostres. Subsequent writers 
have admitted these highly natural subdivisions ; but there has been 
a constant tendency to raise their rank. The genus Crocodilus has 
become the order Crocodilia ; the subgenera Alligatores, &c., have 
been elevated into families ; Dr. Gray has shown that the AJl/igatores 
must be divided into three genera, and that there are at least two genera 
of Crocodili; and, while one of Cuvier’s species of Longdrostres has 
been suppressed, the group is very generally retained with a changed 
name (Gavzalzs), a very important addition having been made to it in 
the Crocodilus Schlegelid of Miiller and Schlegel. 
Unless the considerable materials contained in the British Museum, 
the Hunterian collection, the collection of Dr. Grant, and the Christ- 
‘Church 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. Rolleston for the many facilities they 
have liberally afforded me. 
The recent species of the order Crocodilia are divisible into three 
families, which correspond with the original subgenera of Cuvier, and 
may be termed the Al@gatoride, the Crocodilide, and the Gavialide. 
I. In the ALLIGATORID 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 received into pits in the margins of the premaxilla and 
maxilla ; while the mandibular teeth behind these pass inside, and 
not between, the mawxillary 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. 
This family embraces three genera, readily distinguishable by 
osteological characters—AUMigator, Caiman, and Jacare. 
Genus 1. ALLIGATOR. 
Dental formula, “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 perfrontal and lach- 
rymal bones. The aperture of the external nares is divided into two 
