a Pachypod from the Cambridge Upper Oreensand. 307 



the accuracy of the method of research. It therefore seems 

 desirable that fossil groups should be comparable in magni- 

 tude with the genera and species of true {i. e. living) Reptilia. 



Probably the Folkestone fossil and these from Cambridge 

 occur upon the same horizon ; for the Cambridge animals are 

 usually from the upper portion of the phosphatic stratum, and 

 are rarely mineralized with phosphates, while the Acantho- 

 pholis horriduSj according to Mr. Etheridge *, is from the 

 Chalk-marl, about 8 feet above the Upper Greensand ; and 

 almost all the marine species found in the bed, except Ammo- 

 nites and some of the Echinoderms, are also fossils of the 

 Cambridge Greensand. 



The English Dinosauroids of which the foot-bones have 

 hitherto been figured are referred to Hylceosaurus^ Iguanodon^ 

 Scelidosaurus, and Hypsilophodon. The metatarsus in Hylceo- 

 saicrus is made of three somewhat slender and greatly elon- 

 gated bones f* In Iguanodon there are three principal meta- 

 tarsal bones, which are less elongated and relatively much 

 stouter than in the specimen referred to Hylceosaurus^ while 

 there is also a rudimentary slender fourth metatarsal J. In 

 Scelidosaurus there are four moderately elongated metatarsals, 

 of which the first is conspicuously short ; and there is also, 

 according to Professor Owen, a slender styliform rudiment of 

 a fifth metatarsal, which is adherent to the proximal end of 

 the fourth § ; while in the skeleton which Professor Huxley 

 refers to Hypsilopliodon (Quart. Journ. Geol. Soc. Feb. 1870) 

 the animal is remarked upon as possessing certainly four, and 

 perhaps also a slender fifth metatarsal bone, which, from 

 Prof. Owen's figure ||, appear to be about as long as 2\ cen- 

 trums of dorsal vertebra, and rather more slender than the 

 metatarsus of Scelidosaurus. When, therefore, the foot of 

 Acanthopholis was found to consist of five well-developed 

 bones, of which the fifth appears well capable of carrying 

 phalanges, and the first is singularly massive, the animal was 

 invested with platypodial interest, as probably showing a cha- 

 racter new in the order, and offering a new point of affinity. 



At the time in which Prof. Owen wrote (1857) some doubt 

 hung over the determination of the terminal segments of the fore 

 and hind limbs ; and this doubt is not to be neglected in inter- 

 preting the present specimens, notwithstanding the researches 

 of Leidy, Cope, and Huxley on the proportions of the Dino- 

 saurian limbs. 



* Geol. Mag. 1867, vol. iv. p. 68. 



t Wealden Kept. 1857, part 4, pi. xi. | Loc, cit. pis. i.-iii. 



§ Oolitic Kept. 1862, part 2, p. 17, pi. x. 



II Wealden Dines. 1854, pt. 2, pi. i. 



