184 ON REMAINS OF AN EXTINCT SAURIAN, 
expanded snout than any of the crocodilide. In this feature it 
reminds us rather of the American alligators, Caiman and Jacare. 
Of the sockets posterior to the notch, the tenth is distinctly 
the largest; it is however nearly equalled in size by the eleventh, 
and the latter is, as in johnstoni, much larger than the ninth. 
Bearing in mind that in the crocodiles and the alligators the 
eleventh lower tooth is the largest, we must recognize in this 
character of the fossil species a mark of divergence from both 
of the great recent families with which it can possibly be 
compared. 
Seeing that this mandible has nothing in common with that 
of a gavial, it is almost needless to say that the splenial does not 
enter into the symphysis 
EXTREMITY OF THE LEFT MANDIBLE OF AN ADULT. 
(NATURAL SIZE.) 
Puate XIII. 
It is evident that no increase in the width of the symphysial 
region, as obtains in C. porosus, took place during the growth of 
the post-pliocene reptile, since, in this subject, the proportions 
of the young mandible are strictly preserved. The side of the 
notch presents a well marked groove for the reception of the 
upper fourth tooth, and behind ita similar impression appar- 
ently due to the action of the fifth. These lateral grooves are 
probably a character of old age, since they are not found in an 
adolescent mandible, nor in the subject of Plate X., Figure 1. The 
sixth tooth, in place but imperfect, is remarkably small, its diame- 
ter being but little more than half that of the seventh socket. So 
great a difference in size between these teeth may be abnormal 
or senile—it does not exist in the younger phases of the jaw. 
ARTICULAR REGION OF RIGHT MANDIBLE, ADULT. 
(NATURAL 8I1ZE.) 
PuaTe XII. 
The most obvious characters of this bone are the breadth and 
flatness of the upper surface of the surangular, and the great 
