446 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [DoC. ] 5, 



small scutes, or that anything but soft parts united the dorsal with 

 the ventral shield. 



Such are the chief modes in which the dermal armour of the 

 CrococUlia is disposed. With respect to the form and mode of union 

 of the component scutes, it does not appear that many general rules 

 can be laid down. The scutes are, however, always disposed sym- 

 metrically with regard to the median planes of the back and belly, in 

 such a manner that the middle line answers to the interval or suture 

 between two longitudinal rows of scutes*. 



The dorsal scutes almost always present a more or less marked 

 longitudinal ridge externally, while the ventral scutes, when they 

 exist, have either flat and smooth, or evenly curved, external 

 surfaces. 



In some procoelian recent Crocodilian such as Crocodilus acutus, 

 there are no ventral osseous scutes. The dorsal scutes, on the other 

 hand, are well developed ; they are either square, pentagonal, or 

 hexagonal, and their lateral edges are very irregular and jagged. I 

 cannot find in any case, however, that they interlock so as to unite 

 suturally, — a greater or less portion of the dermis being in all cases 

 interposed between their edges. The scutes nowhere overlap, and, 

 as might be expected, they exhibit no articular facets. 



Each scute presents externally a strong longitudinal ridge, which 

 lies on the outer side of the median line, and cuts the hinder margin 

 of the scute posteriorly, while anteriorly it subsides into the general 

 surface at some distance from the anterior margin. The highest 

 point of the ridge is far nearer the posterior than the anterior margin. 



The inner faces of the scutes are smooth, concave from side to side, 

 and slightly convex from before backwards. 



Scattered about between the ventral and cervical, and the cervical 

 and dorsal shields, there are many small and irregular detached 

 scutes, of all sizes down to |-ths of an inch in length. The smallest 

 of them are simply incipient ossifications in the dermis which under- 

 lies the ridges of the epidermic scales, and they present no sculpture. 

 In fact they correspond with the apices of the ridges of the larger 

 scutes. In some of larger size, which present a certain' amount of 

 sculpture, the apex of the ridge is altogether posterior, and the scutes 

 very closely resemble the smaller irregular angulated scutes of 

 ^tagonolepis. 



Other existing procoelian Crocodilia present a far more complete 

 dermal armour ; and certain Alligators, of the genus or subgenus 

 Jacaref, are not surpassed, so far as I am aware, by any recent 



* The only exceptions to this rule that I am acquainted with are offered by 

 the scutes of the median caudal crest, and by a small extent of the dorsal region 

 of the tail, just in front of the point of convergence of the lateral crests. Here 

 there is a variable number of scutes, which lie one behind the other, gradually 

 diminishing in size, in single series, so that their centres correspond with the 

 median line. 



t Alligator lucius, like Crocodilus 'vulgaris, has no ossified ventral scutes. 

 Caiman ;palpebrosus has ventral scutes like those of Jacare, of which I have 



