158 REPORT— 1841. 



distal end the transverse section exhibits the form of a plate bent towards the 

 fibula, and its narrowest transverse diameter is 2| inches. 



The portion of tlie fibula is 11^ inches long. In the middle it is flat on 

 one side, slightly concave on another, and convex on the two remaining sides. 

 It presents the same cancellous structure as the tibia, but the concentric ar- 

 rangement of the layers of cells is more exact. Towards the opposite end of 

 the bone the concave side becomes first flat, and is then produced into a con- 

 vex wall, terminating one end of a transverse section of a compressed and 

 bent thick plate of bone. 



Metatarsals. — These bones exhibit the characteristic irregularity of length 

 of the Crocodilian metatarsals. Of two imbedded in the rock, and apparently 

 the innermost and second, of the left hind-foot, the former or smaller measured 

 1 foot in length and the latter 2 feet, having a diameter of 8 inches at its 

 greater end, and of 4 inches 5 lines at its narrowest or middle part, and of 

 G inches at its other extremity, Avhich was imperfect. The whole of the bone 

 within the compact outer crust consisted of cells varying from a half to two- 

 thirds of a line in diameter. Portions of four other detached metatarsals are 

 described. 



Ilia, Ischia, Pubis, and Coracoid Bone. — These bones conform in the main 

 to the Eiialiosaurian type. The remains of the ilia are flat and nearly straight, 

 and they gradually but slightly widen towards one end. Of one ilium a por- 

 tion, 25 inches long and 10 inches across at the broadest end, is preserved, 

 and of the other a I'ragment 20 inches in length. 



The mesial extremities of the pubis and ischium are preserved in the same 

 block of stone. The pubis differs from the Crocodilian type in its greater 

 breadth. The portion exposed in this block is principally convex, but it be- 

 comes concave towards the opposite or median margin. At its broadest part 

 it is 13 inches across, and its length is 17 inches. This expanded extremity 

 is rounded, and the diameter of the corresponding expanded extremity of the 

 ischium, which is obliquely truncated, is 9 inches. In another block of stone 

 the expanded extremity of the opposite pubis is preserved, and measures 14 

 inches across and 22 inches in length. 



The bone which bears most resemblance to a coracoid is 2 feet in length 

 and 17 inches in its greatest breadth, and it varies in thickness from 3 to 5 

 inches. The breadth of this bone indicates the great development of the 

 muscles destined for the movement of the fore-leg, whence it may be inferred 

 that the anterior extremities were more powerfully and habitually used in pro- 

 gressive motion than in the Teleosaurian Crocodiles. 



It will be sufficiently apparent, from the brief notice of the principal cha- 

 racters of these interesting remains here given, that they cannot have be- 

 longed to any of the genera of the great ambulatory terrestrial Dinosaurs ; 

 and, on the other hand, the length, thickness, and form of the condyles of 

 the femur, and the size and shape of the metatarsal bones equally remove the 

 Enaliosaurs from the pale of comparison. 



There then remain, as claimants of the fossils in question, first, the great 

 Mosasaunis of the Cretaceous formations, the locomotive extremities of 

 which have not been yet discovered ; secondly, the equally gigantic Cetio- 

 saurus brcvis, associated with the lyuanodon in the Wealden, and, from its 

 or"-anization, more likely than the Iguanodon to be found in later marine de- 

 posits ; finally, the Reptile of the Maidstone greensand, to which the name of 

 Polyptychodon has been provisionally assigned from the configuration of its 

 teeth. But, since the teeth of the geims Cetiosaurus are not yet determined, 

 the identity of this genus with Polyptychodon is open to suspicion ; and sub- 

 sequent discoveries may demonstrate that the great Saurian of the Hythe 



