IXXXU PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



Lophiodonts are the most artio-dactyloid of the Perissodaetyles, no 

 particular hypothesis is advocated ; there can be but one inference 

 from this and the numerous analogous facts that have already been 

 made known. So, likewise, in regard to the typical character of 

 dentition as manifested by the number and kind of teeth, we find, in 

 this last Eocene mammal which has come to light, a repetition of 

 that remarkable adherence to a more general mammalian character. 

 The older Oolitic mammals exemplify a tendency to a type of den- 

 tition of a still higher generality than the mammalian class." In 

 this manner three genera of the Oolitic epoch resemble in their den- 

 tition the general Vertebrate type, whilst no less than 38 genera, 

 belonging to the Eocene epoch, resemble in dentition the Mammalian 

 Diphyodont type ; but Professor Owen adds that " all general rules 

 in organic nature have their exceptions, and differ in that respect 

 from inorganic phenomena, in regard to some of the general laws of 

 which no exceptions have been as yet discovered." If we consider 

 this gradual change, from a more general type of vertebral organiza- 

 tion to a more special type, to be the result of original creation, it 

 seems difficult to understand the possibility of exceptions to any great 

 law ; but if it be considered only as the progressive modification of 

 some type from a long series of ages of existence, it would seem quite 

 natural and probable. The fact, however, though so strongly sup- 

 ported by Professor Owen, has been disputed in a paper, to be sub- 

 sequently noticed, by Dr. Ealconer, and the Professor has promised 

 to consider at a future day trie objection thus taken to his theory, 

 which is unquestionably one of great importance in speculative Pa- 

 laeontology. A description of some of the bones of the extremities 

 terminated this most interesting paper, and assisted to confirm the 

 determination of the true position and affinities of Pliolophus, and 

 most probably of Byracotheriwn, also in the Ungulate series. 



The bones of the hind foot of an Iguanodon, discovered by Mr. 

 Beckles in the Wealden-clay of the south coast of the Isle of Wight, 

 afforded materials for another short paper by Professor Owen. After 

 stating the result of his investigation of these interesting relics, he 

 observes, — "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 Igua- 

 nodon, 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 ;" a modification of the hind foot, he adds, which 

 is interesting by its analogy to the tridactyle hind foot of the Rhi- 

 noceros and Tapir, and still more so by its correspondence in the 

 varying number of the phalanges, and their progressive increase 

 from the inner to the outer toe, with the foot of birds, — a fact which 

 naturally suggests a caution in respect to the habit of referring the 

 many large tridactyle impressions found in the Wealden and other 

 formations, to the class of Birds. 



A large femur, also found in the Weald-clay of Sandown Bay, Isle 



