1857.] GIBSON 1GUANODON. 175 



metatarsus of a horse, to have terminated in a point, and not to have 

 supported a rudimental claw. The outer side of the outermost 

 metatarsal shows no mark of any other bone, rudimental or other- 

 wise, having been there attached. The co-articulating surfaces at 

 the proximal ends of the metatarsals show them to have belonged, 

 as their position in the matrix indicated, to the same foot. 



The innermost supports a toe of three phalanges, the middle 

 metatarsal one of four phalanges, the outermost one of five pha- 

 langes. Only the ungual phalanx of the middle toe is wanting : and 

 that no other phalanx is absent from this toe is shown by the modi- 

 fication of the distal articular surface of the penultimate phalanx ; 

 which, like that in the adjoining toes, is less concave transversely, or 

 is more uniformly convex, than the distal trochlear surfaces of the 

 more proximal phalanges. 



The modifications of the claw-phalanx of the outer and inner toes 

 accord with those of the larger and previously discovered claw- 

 phalanges of the Iguanodon. 



Guided by the analogy of the number of phalanges in the toes of 

 the hind-foot of the Iguana, we may infer that the three toes that 

 are normally developed in the hind-foot of the Iguanodon, are the 

 second, third, and fourth ; that the first or innermost is represented 

 by a rudimental metatarsal, which was concealed beneath the skin of 

 the foot ; and that the fifth or outermost was entirely suppressed. 



This modification of the hind-foot is interesting by its analogy to 

 the tridactyle hind-foot of the Rhinoceros and Tapir ; and still 

 more so by its correspondence in the varying number of the pha- 

 langes, and their progressive increase, from the inner to the outer 

 toe, with the foot of birds. 



It adds to the probability of Mr. Beckles's idea of the Iguanodon- 

 tal nature of the large tridactyle impressions which he has discovered 

 and described in certain Wealden formations, and suggests caution as 

 to inferring that tridactyle impressions, showing a progressive increase 

 of digital joints from three to five, from the innermost to the outer- 

 most toes, must, therefore, necessarily belong to the class of Birds. 



10. Notice of the Discovery of a Large Femur of the Iguano- 

 don in the Weald Clay at Sandown Bay, Isle of Wight. 

 By T. F. Gibson, Esq., F.G.S. 



[Abstract.] 



In the year 1829 a paper was read before the Society by Dr. Buck- 

 land, giving an account of the first discovery in the Isle of Wight of 

 the bones of the Iguanodon. The paper described particularly a meta- 

 carpal bone of this animal discovered by Dr. Buckland in Sandown 

 Bay, " in the iron- sand," to use his own words, " which forms the 

 shore there, a little east of Sandown Fort, between high and low 

 water," and he states his belief that it was the largest bone of this 

 description that had then been found. 



In the month of October last, an unusually high tide and violent 



