272 PALEONTOLOGY 



Siib- Order 2. — Opisthocoelia.* 



The small group of Crocodilia so called is an artificial one, 

 based upon more or less of the anterior trunk vertebrae being 

 united by ball-and-socket joints, but having the ball in front, 

 instead of, as in modern crocodiles, behind. Olivier first 

 pointed out this peculiarity t in a Crocodilian from the 

 Oxfordian beds at Honfleur, and the Kimmeridgian at Havre. 

 The writer has described similar opisthocoelian vertebrae from 

 the great oolite at Chipping Norton, from the upper lias of 

 Whitby, and, but of much larger size, from the Wealden for- 

 mations of Sussex and the Isle of Wight. These specimens 

 probably belong, as suggested by the writer in 1841, \ to the 

 fore part of the same vertebral column as the middle dorsal 

 vertebra 3 , flat at the fore part, and slightly hollow behind, on 

 which he founded the genus Cdioscmrus. The smaller opis- 

 thocrelian vertebra 3 , described by Cuvier have been referred by 

 Yon Meyer to a genus called Streptosiwndylus. 



In one species from the Wealden, dorsal vertebrae measur- 

 ing 8 inches across are only 4 inches in length, and caudal 

 vertebrae nearly 7 inches across are less than 4 inches in length. 

 These characterize the species called Cetiosaurus brevis.§ 



Caudal vertebrae measuring 7 inches across and 5i- inches 

 in length, from the lower oolite at Chipping Norton, and the 

 great oolite at Enstone, represent the species called Cetiosaurus 

 medius. 



Caudal vertebrae from the Portland stone at Garsington, 

 Oxfordshire, measuring 7 inches 9 lines across and 7 inches 



* Opiethoe, behind ; hoilos, hollow ; vertebra concnve behind, convex or lint 

 in front 



f Annalos tin Musrum. torn, xii., p. S,'5, pi. x. xi. 



J " Report on British Fossil Reptiles," Trans. Brit. Assoc, for 1841, p. %. 



# They have since been referred to the dinosaurian order under the name 

 of Pelorosaurus, but without any evidence of the true sacra] characters of 

 i hat order: the cavities of long bones are common to < 'roeodilians and THno- 



BAlirfl. 



