ON FOSSIL AND RECENT REPTILIA. 165 



of the same vertebral column as the vertebrae, flat at the fore part, and slightly 

 hollow behind, on which he founded the genus Cetiosaurus. The smaller 

 opisthoccelian vertebrae described by Cuvier have been referred by Von 

 Meyer to a genus called Streptospondylus. 



In one species of Cetiosaurus from the Wealden, dorsal vertebra?, 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 vertebras, 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 in length, have been referred to the 

 Cetiosaurus longus ; the latter appears to have been the most gigantic of 

 Crocodilians. 



Suborder Proccelia*. 



Crocodilians with cup-and-ball vertebra? like those of living species first 

 make their appearance in the Greensand of North America (Croc, basifissus 

 and Croc. basitruncatus)\. In Europe their remains are first found in the 

 tertiary strata. Such remains from the plastic clay of Meudon have been 

 referred to Crocodilus isorhynchus, Croc, ccelorhynchus, and Croc. Becquereli. 

 In the ' Calcaire grossier ' of Argenton and Castelnaudry have been found the 

 Croc. Rallinati and Croc. Dodunii. In the coeval eocene London Clay at 

 Sheppey Island, the entire skull and characteristic partsof the skeleton of Cro- 

 codilus toliapicus and Croc. Chanrpsoides occur. In the somewhat later eocene 

 beds at Bracklesham occur the remains of the Gavial-like Croc. Dixoni. In 

 the Hordle upper eocene beds have been found the Crocodilus Hastingsia 

 with short and broad jaws; and also a true Alligator (Croc. Hantoniensis). 

 It is remarkable that forms of proccelian Crocodilia, now geographically re- 

 stricted — the Gavial to Asia, and the Alligator to America, — should have been 

 associated with true Crocodiles, and represented by species which lived during 

 nearly the same geological period, in rivers flowing over what now forms the 

 south coast of England. 



Many species of proccelian Crocodilia have been founded on fossils from 

 miocene and pliocene tertiaries. One of these, of the Gavial subgenus (Croc, 

 crassidens) from the Sewalik tertiary, was of gigantic dimensions. 



Order X. Laceiitilia. 



Vertebrae proccalian, with a single transverse process on each side, and 

 with single-headed ribs: sacral vertebrae not exceeding two. 



Small vertebrae of this type have been found in theWealden of Sussex. They 

 are more abundant, and are associated with other and more characteristic 

 parts of the species in the Cretaceous strata. On such evidence have been 

 based the Raphiosaurus subulidens, the Coniosaurus crassidens, and the 

 Dolichosaurus longicollis. But the most remarkable and extreme modification 

 of the Lacertian type in the Cretaceous period is that manifested by the huge 

 species, of which a cranium, 5 feet long, was discovered in the Upper Chalk 

 of St. Peter's Mount, near Maestricht, in 1780. This species, under the name 

 Mosasaurus, is well known by the descriptions of Cuvier. Allied species 

 have been found in the cretaceous strata of England and N. America. The 

 Leiodon anceps of the Norfolk chalk was a nearly allied marine Lacertian. 

 The structure of the limbs is not yet well understood ; it may lead to a sub- 

 ordinal separation of the Mosasauroids from the Land-lizards, most of which 



* irpb, before ; icotXos, hollow : vertebrae with the cup at the fore part and the ball behind, 

 t Quarterly Journal of the Geological Society, January, 1849, p. 380. 



