I94 REPORT — 1841. 



that the deposition of the cretaceous beds was related to the formation of the 

 Wealden group by proximity of time as well as place. The terrestrial group 

 of gigantic Reptiles receives in the Wealden an accession of two new genera, 

 viz. Hylceosaurus and Megabsaurus ; and the remains of both these, and 

 especially of the Iguanodon, are so abundant, that the Wealden strata may 

 be regarded as the metropolis of the Dinosaurian order *. 



The amphibious Crocodiles might be expected, from their known habits at 

 the present day, to liave left abundant evidences of their remains in strata, 

 which seem to have been deposited at the estuary or mouth of some great 

 river ; in a climate, indicated by its vegetable fossils to have been warmer or 

 more equable than at present ; and during a period of time which permitted 

 the accumulation of 1000 feet of strata. Accordingly, the Crocodilian order 

 of Reptiles has been found to be represented by several distinct genera in the 

 Wealden formations. 



Some new characters and modifications of structure might also have been 

 anticipated in those Crocodilians which existed at a period antecedent to the 

 deposition of about 1500 feet of cretaceous strata, which, again, preceded the 

 formation of the whole series of superimposed tertiary and diluvial beds. 

 Nevertheless, the remarkable modifications which all the Wealden Crocodi- 

 lians present in the structure of their vertebrae, as compared with the Eocene 

 and existing Crocodiles, could not have been anticipated ; and even now that 

 they are ascertained by repeated observation, some of them still remain in- 

 explicable in relation to any conjectural habits of the species, or hypotheti- 

 cal conditions under which they actually existed. We may understand why 

 the ball-and-socket articulation of the vertebras of the present amphibious 

 Crocodiles frequenting dry land, should be exchanged for a "joint having 

 elastic substance included between two concave articular surfaces, as a struc- 

 ture better adapted to Crocodiles more habitually living and moving in water ; 

 but these Crocodiles Avith biconcave vertebra are associated with others having 

 plano-concave vertebrae, and also with a species having vertebrae joined by 

 ball-and-socket articulations. And the difficulty is not diminished by the re- 

 markable fact of the latter structure being the rererse of that in i-ecent Ci"o- 

 codiles, the ball and the cup having changed places in the extinct Strepto- 

 spmidylus ; and having assumed the position which they present in certain 

 Sauroid fishes, and in the dorsal and cervical vertebrae of some of the herbivo- 

 rous Mammalia. 



The biconcave, plano-concave, and convexo-concave modifications of the 

 vertebrae are not the only points in which the extinct Crocodilians of the 

 Wealden strata diflPer from those of the London clay and from the existing 

 species. The genus GoniophoUs, for example, exhibits a remarkable deve- 

 lopment of its dermal armour, the large quadrangular scutes of which, inter- 

 locked by teeth received into depressions, are gigantic representations of the 

 scales of some of the Ganoid fishes ; Avhile the smaller hexagonal and penta- 

 gonal scutes t were articulated together by marginal sutures, as in the dermal 

 bony covering of the armadillo. The Poikilopleuron exhibits a medullary 

 cavity in the body of the vertebrae, and a double origin of the spinous pro- 

 cess. The Suchosaurus offers a very striking change in the form of the 



* Dr. Mantell calculates that not less than seventy individuals of the Iguanodon, varying 

 in age and magnitude, from the young just escaped from the shell to the mature animal, with 

 a femur of more than a yard in length, have come under his examination ; and he justly oh- 

 serves that " more than thrice that number have, in all probability, been destroyed by thg 

 workmen, and altogether eluded the observation of the PaJjeoutologist." — See his Memoir in 

 the Philosophical Transactions, 1841. 



t These have been discovered since the first sheets of this Report went to press by my 

 friend Mr. Holmes of Horsham, in the Wealden strata neai- that town. 



