BY C. W. DE VIS, M.A. 189 
and differentiated armature of the other two families. A glance 
at the sockets im the fossil jaws, and the numerous teeth scat- 
tered through the drift, will convince us that the species repre- 
sented by them belong to one or other of the predominant 
members of the order; not only do the teeth vary greatly in 
size and position conformably to those of crocodiles, but they 
afford sufficient evidence that their form in the hinder part of 
the series was almost the same as that distinguishing the 
posterior from the anterior teeth of living crocodilia. It is, 
however, remarkable that these teeth with constricted crowns 
and short lobes are exceedingly scarce—they number three per 
cent. only in a collection of 450 specimens of all ages. It is 
difficult to believe that this paucity is altogether accidental, it 
would indeed be preferable to infer that not more than one or 
two teeth on each side took on this character, which in C. porosus 
is a character of immaturity. 
EXOSKELETON. 
Prate XV. 
Students of past life are indebted to Professor Huxley, for the 
observation (Proc. Lin. Soc. Lond., iv., p. 21) that in two of the 
genera of alligatoride, Caiman and Jacare, the lateral edges of 
all the scutes of the dorsal and ventral shields are united by 
serrated sutures, and the anterior end of the outer face in each 
is provided with a well marked smooth facet, which is over- 
lapped by the smooth under surface of the scute in front of it ; 
while in alligator, the crocodiles and the gavials, the edges of 
the scutes, except those of the two median longitudinal rows, 
are hardly ever united by sutures, and there is no flat bevelled 
articular face on the outer surface of the anterior margin of a 
scute for articulation with its predecessor. Of the fossil scutes, 
to be interpreted by the light of this statement, five kinds may 
be distinguished—the first quadrangular in shape with the lateral 
edges serrated, the fore edge bevelled and forming a distinct 
articular plane of variable width, and with a more or less 
) 
