ON THE DERMAL ARMOUR OF JACARE AND CAIMAN 295 
represent the chevron bones of the other caudal vertebra, but are 
not united below. 
The dorsal scutes have the arrangement which has often been 
described. They are separated (except perhaps the median rows) 
by integumentary spaces, neither overlapping nor uniting by sutures ; 
and there are no ventral scutes. 
Among the osteological characters which have been detailed, the 
peculiarities of the tergal armour, the proportions of the skull, com- 
bined with the characters of the ridges upon its surface, and the form 
of the premaxillo-maxillary suture amply suffice to diagnose this 
species. Even in the small skull, only 54 inches long, lent to me by 
Dr. Gray, the characteristic features of the species are well exhibited, 
although age appears to give rise to many differences. Thus the 
posterior margin of the external nostrils does not extend so far back 
as in the adult, and the facial is smaller in proportion to the syncipital 
region, whose anterior and posterior transverse dimensions are very 
nearly equal. The orbits are proportionally larger, the interorbital 
space more excavated ; and the outer straight margins of the supra- 
temporal fossz are parallel with the longitudinal axis of the skull. 
Still more important differences are visible on the palatine face of the 
skull. The premaxillo-maxillary suture reaches back, indeed, to the 
line of the seventh tooth; but it forms an even curve whose summit 
is in the middle line. The aperture of the posterior nares, again, has 
a totally different form from that which it assumes in the adult. It is 
somewhat heart-shaped, with its apex forwards, measures } inch long 
by ,3,ths at broadest, and looks altogether downwards, while its 
anterior margin is situated far more forward in the palate than that 
of the adult. 
2. Crocodilus biporcatus. 
This, the best-known Crocodile, is a very well-marked species, 
characterized (beside the peculiarities of its dermal armour) by a 
comparatively slender skull, similar in shape to that of C. vulgaris, 
and, like it, without any sudden enlargement immediately behind the 
canine groove ; and by the strong ridge which arises on each lachry- 
mal bone close to the anterior edge of the orbit, and is continued 
forwards on to the line of junction of the nasal and mawillary bones, 
so that the naso-maxillary suture traverses the axis of the ridge, and 
then curves outwards, descending towards the alveolus of the tenth 
tooth. The premanxillo-manillary suture is W-shaped ; and its salient 
angles reach backwards even to the level of the posterior margin of 
the seventh alveolus. 
