^10 ON THE ARMOUR OF EXTINCT REPTILES. [May 26, 



median plates. The last specimen is a fragment about 2 inches 

 wide and half an inch thick at the margin, much thinner at the 

 fracture, and without indication of boss or pit, so that its position 

 cannot be located. 



We can only regret the imperfections of this evidence of 

 dermal armour, but when I saw the remains they had already 

 been removed for some time from the rock, and it is certain that 

 they would have been carried away by the torrential drainage in 

 the wet season, but for the interest taken by Mr. Van Renen in 

 their preservation. 



This armature differs from that of Pareiascmrus haini, first 

 in the elongated form of the median scutes, secondly in the 

 presence of the central truncated boss with the depression behind 

 it, and thirdly in the radiated ornament — features which are 

 absent from Pareiasaurus haini. In that species the anterior 

 median scutes appear to be subcii-cular, or subquadrate, with a 

 few circular vascular openings or small pits ; but in the later 

 plates no ornament is recognised, and the plates appear to be 

 thinner and arched outward. 



The caudal vertebra is fi'om a position between the fifth and 

 tenth in the tail. This early position is indicated by the trans- 

 verse width of the anterior face of the centrum exceeding its 

 vertical depth (text-fig. 127); by the strong vertically compressed 

 lateral ridges above the transverse processes for the caudal ribs, 

 which are directed outward and slightly downward ; by the large 

 size of the transverse posterior facet for the chevron-bone, which 

 gives the centrum the aspect of being obliquely crushed from front 

 to back (text-fig. 129) ; and by the vertical position of the pre- 

 zyga-pophyses, with the facets looking inward and upward (text- 

 fig. 127). 



When this centrum is compared with the earlier tail-vertebrse 

 of Pareiasaurus haini the centrum is shorter from front to back, 

 for it only measures one inch ; and in the species referred to, the 

 measurement is always longer when the anterior face of the 

 centi^um is wider than deep. The neural canal is smaller (text- 

 fig. 128), as in later caudals of Pareiasaurus haini. These dif- 

 ferences would indicate a shorter tail with less lateral movement. 



The neural arch is not distinctive. The neural spine is broken 

 away, but its base has the usual triangular form. The anterior 

 articular face of the centrum is roughly hexagonal with the 

 margin slightly rounded, and a moderate central concavity. It is 

 1^ inch wide and 1^ inch deep. The posterior face is rather 

 smaller and rather more concave. It is roughly four-sided, with 

 the lateral margins approximating suj^eriorly (text-fig. 128). 

 It is 1-jL- inch deep, 1-j^ wide above the chevron articulation, and 

 1 inch wide on the neural canal. The oblique surface for the 

 articulation of the chevron-bone measures half an inch from 

 front to back, and extends over the width of the vertebra which 

 it truncates. 



