WEALDEN FORMATIONS. 43 



faintly divided by a median vertical rising ; the rounded edge of the articular 

 surface is slightly raised, and is interrupted on both sides by smooth shallow com- 

 mencement of the curved vascular groove ; this deepens and contracts as it extends 

 forwards. The upper surface of the phalanx is convex longitudinally and transversely ; 

 the lower surface is rather more convex transversely than the upper, but is slightly 

 concave longitudinally. The upper and lateral surfaces, for about an inch near the 

 base, are deeply sculptured by large irregular longitudinal grooves and ridges ; the 

 rest of the upper surface is impressed by fine interrupted longitudinal impressions, 

 but having, on the whole, a smooth appearance. The laminated superposition of the 

 exterior compact portion of the bone is shown by the separation of portions of the 

 layers of about one line in thickness. The under surface is more deeply impressed by 

 cavities having reticulate elevations. The right aliform process begins 10 lines from 

 the articular surface, the left about 14 lines from the same part; this base is bounded 

 below by slight impressions, and above by the lateral canals, which appear to sink into 

 the bone. A few distant vascular grooves mark the upper surface of the bone, but 

 more numerous larger ones are situated near the lateral canals and at the broken ante- 

 rior end of the phalanx. The following are its dimensions : 



Transverse diameter of bone .... 



Transverse diameter of broken end .... 

 Vertical diameter of base .... 



Vertical diameter of broken end .... 



LeDgth to broken end .... 



The largest phalanx of this kind which has hitherto come under my observation is 

 one (Tab. XVI, fig. 2) which had been washed out of the same tidally submerged 

 Wealden iron-sandstone, which forms the shore between high and low water to the east 

 of Sandown Fort, Isle of Wight. This phalanx had been rolled and waterworn, like 

 most of the saurian fossils from that locality. The margins of the articular base of the 

 phalanx are thus rounded off, and those of the sides and extremity have been worn 

 away, rendering the latter more obtuse. Nevertheless, in this state, the phalanx 

 measures 6 inches in length and 4^ inches in breadth, much surpassing in size the 

 largest ungual phalanx of the elephant, mammoth, or mastodon. It would be 

 unsafe, however, to infer from the size of a claw or the bone supporting it that of the 

 entire animal ; an ungual phalanx presents very different proportions to the rest of the 

 limb and to the entire animal, in different species : that of a horse, e.g., exceeds in 

 size that of an elephant : and the ungual phalanx of a sloth is longer than that of 

 the largest crocodile. In the general proportions, and broad subdepressed form 

 of the bone here described, it resembles the more perfectly preserved ungual 

 phalanges known by their association with other parts of the skeleton to have 



In. 



Lines 



3 



5 



2 



2 



2 



7 



1 



6 



4 



4 



