OWEN.—CLASSIFICATION OF REPTILIA. 85 
Hastingsice, with short and broad jaws ; and also a true alligator (C. Hantoniensis), 
itis remarkable that forms of proccelian Crocodilia, now geographically restricted, 
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 cvast of Eng 
land. Many species of proccelian Crocodilia have been founded on fossils from 
miocene and pliocene tertiaries. One of these, of the gavial sub-genus (0. 
erassidens), from the Sewalik tertiary, was of gigantic dimensions. 
Order X. Lacertilia.—Vertebrz, in most, procelian, with a single transverse 
process on each side, and with single-headed ribs ; sacral vertebree, not exceeding 
two. Small vertebre of this type have been found in the Wealden 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 Rhapiosaurus subulidens, the Coniasaurus crassidens, and the Dolichosaurus 
longicollis. But the most remarkable and extreme modifications of the lacertian 
type, in the eretaceous period, is that manifested by the huge species of which a 
cranium, five 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 North 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 are represented by existing species, in which a close 
transition is manifested to the next order. 
Order XI. Ophidia—Vertebre very numerous, proccelian, with a single trans- 
verse process on each side; no sacrum; no-visible limbs. The earliest evidence, 
at present, of this order is given by the fossil vertebre of the large serpent 
(Paleeophis, Ow.) from the London clay of Sheppy and Bracklesham. Remains 
of a poisonous serpent, apparently a Vipera, have been found in miocene deposits 
at Sansans, south of France. Ophidiolites, from (iningen, have been referred to 
the genus Coluber. 
Order XII. Chelonia.—The characters of this order, including the extremely 
and peculiarly modified forms of tortoises, terrapenes and turtles, are sufficiently 
well known. The chief modifications in oolitic Chelonia known to Prof. Owen 
were the additional pair of bones, interposed between the hyosternals and hypos- 
ternals of the plastron, in the genus Pleurosternon from the Upper Oolite at 
Purbeck. It would be very hazardous to infer the existence of reptiles, with the 
characteristic structure of the restricted genus Testudo, from the foot-prints in the 
triassic sandstone of Dumfries-shire. But Prof. Owen concurred in the general 
conclusions based upon the admirable figures and descriptions in the splendid 
monograph by Sir Wm. Jardine, Bart., F.R.S., that some of those foot-prints most 
probably belonged to species of the Chelonian order. As enormous species of 
true turtle (chelone gigas), the skull of which measured one foot across the back 
part, had left its remains in the eocene clay at Sheppy. The terrestrial type of 
the order had been exemplified on a still more gigantic seale by the Colossochelys 
of the Sewalik tertiaries, 
