ON BRITISH FOSSIL REPTILES. 141 



This phalanx is slightly bent downwards ; the under surface being concave 

 longitudinally, but convex from side to side ; less so than on the upper surface. 

 The under surface is rough ; the upper surface nearly smooth, except at the 

 margin of the articular surface, on the projecting sides and at the distal ex- 

 tremity, which is sculptured by irregular vascular grooves and holes. The 

 phalanx has a slight oblique twist to one side, and is somewhat thinned off to 

 that side on which the curved groove is longer than on the other side. 



In Mr. SauU's museum is an ungual phalanx of an Iguanodon, which nearly 

 equals those from Horsham, and presents the same subdepressed form. The 

 base is slightly convex transversely ; more concave vertically : the articular 

 surface is faintly divided by a median vertical rising : the rounded edge of 

 the articular surface is slightly raised, interrupted on both sides by the smooth 

 shallow commencement of the curved vascular groove : this deepens and con- 

 tracts as it extends forwards. The upper surface 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 sur- 

 faces, for about an inch near the base, are deeply sculptured bj' 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: 

 their 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 anterior end of the phalanx. The 

 following are the dimensions of this bone : — In. Lines. 



Transverse diameter 3 5 



Transverse diameter of broken end 2 2 



Vertical diameter of base 2 7 



Vertical diameter of broken end 1 6 



Length to broken end 4 4 



it was probably more than 5 inches long when entire. 



The largest of the phalangeal bones in the collection of Wealden Rep- 

 tiles in the British Museum, which from its breadth, slight degree of ob- 

 liquity and vascular canals is referrible to the Iguanodon, is less than those 

 just described. The phalanx in question (No.g^^^, Mantellian Collection) is 

 conical, 4| inches long, probably 5 inches when entire ; but the apex is broken 

 off": the longest diameter of the base or articular surface is 3 inches 3 lines : 

 it is slightly and obliquely compressed, and very slightly curved, and from this 

 circumstance, as well as from the obliquity of the base and its unsymmetrical 

 figure, it probably belonged to the small outer or inner toe at the margin of 

 the foot. Only a small part of the natural smooth articular surface is left, the 

 rest appears to have been scraped away, so that the coarse cancellous structure 

 of the middle of the bone is exposed. The free surface of the bone near the 

 base is deeply sculptured by irregular longitudinal furrows, which served for 

 the implantation of the articular ligaments. The rest of the free surface is 

 tolerably smooth, except at the sides near the apex, where there are numerous 

 oblique outlets for the large vessels and nerves supplying the secreting organ 

 of the claw. The two lateral longitudinal curved grooves which characterize 

 the claws of most Saurians are here well developed ; they commence, one at, 

 the other near, the base ; are at first shallow, then deepen, and finally sink into 



