1858.3 HUXLEY — STAGONOLEPIS. 45X 



internal conformation. At first sight this cmious fossil resembled 

 nothing so much as the crushed and distorted cast of an Orthoceras, 

 but both Mr. Duff and Sir Eoderick Murchison had suspicions of its 

 real nature, and in fact it turns out to be one of the most singular 

 organic remains ever discovered, consistiug of a natural cast of both 

 the dermal bones and the vertebrae of a considerable segment of the 

 tail. 



Loaded by its heavy dermal plates, this caudal fragment appears 

 to have sunk into the fine siliceous mud, the accumulation of which 

 has given rise to the Pindrassie sandstone, and to have been com- 

 pletely permeated therewith, all the cavities left vacant by the putre- 

 faction of the soft parts becoming filled up with a substance which 

 soon hardened into stone. After this had taken place, the bony 

 matter was, by some agency or other (probably the percolation of 

 water), completely removed, so that the fossil, which must have 

 originally laiu loose in a natural mould of the outer surfaces of the 

 caudal scutes (which has unfortunately not been preserved), exhibits, 

 externally, a complete cast of the inner surfaces of a number of suc- 

 cessive transverse series of scutes, and, internally, the casts of the 

 outer surfaces and neural canals of a corresponding number of caudal 

 vertebrae. 



The impressions of the dorsal scutes are but little disturbed, and 

 it is at once obvious that they belonged to the kind which I have 

 named above broad angulated scutes. They form a double series 

 along the dorsal region of the tail, and their inner edges meet along 

 a median sutural line. 



The ventral scutes also appear to have formed only a double series, 

 meeting in the middle line ; but they are much more displaced, the 

 left-hand set being particularly thrown out of position. These 

 scutes are nearly square, and perfectly flat, corresponding exactly in 

 form with the flat scutes already described. It would appear that 

 in the caudal region (as was probably the case in the Teleosaurid) 

 the outer margins of the dorsal and ventral shields came into close 

 contact. 



By the discovery of the true nature of this fragment, the con- 

 clusions to which the structural characters of the different kinds of 

 scutes pointed were completely verified, and I had thenceforward no 

 hesitation in assuming that Stago7iolepis was provided with a dorsal 

 and a ventral dermal shield, composed of scutes resembling those of 

 Jacare, Caiman, Crocodilus Hastingsice, and the Teleosauria, in the 

 manner^in^which their anterior and posterior margins are articulated 

 together. 



With respect to the mode in which the scutes were arranged to 

 form the ventral and dorsal shields, Stagonolepis would appear to 

 have resembled the Teleosauria. The fragment of the ventral shield 

 which I described first is extremely hke a portion of the anterior 

 region of the ventral shield of a Teleosaurus, and it will be observed 

 that it only contains five longitudinal rows of scutes. 



On the other hand, aU the impressions of the hroad and tJiich 

 angulated scutes which I have met with have one lateral margin 



