JURASSIC PERIOD. 539 



The Reptilia have an enormous development in Oolitic 

 times, and are represented both by forms allied to those now 

 in existence and by types which are now altogether extinct. Of 

 the living forms there are as yet no Ophidians, but the Che- 

 lonians are represented by various genera (Idiochelys, Eury- 

 sternum, and Chelone). The Lacertilians are represented by 

 several forms of no special importance, and the Crocodilia were 

 represented by species with amphiccelous vertebras ( Teleosaurus 

 and Steneosaurus). Of the extinct orders of Reptiles, the Ichthyop- 

 terygia, comprising only the genus Ichthyosaurus, form a very 

 marked feature in the Reptilian fauna of the Jurassic period. 

 Numerous species of Ichthyosaurus are known ; and the remains 

 of individuals are very abundant in certain beds, especially in 

 the Lias. The Sauropterygia are represented by numerous 

 species of Plesiosaurus, remains of which are also very abun- 

 dant in the Lias and in other parts of the Oolitic series. The 

 Pterosauria are represented by all their chief genera (Ptero- 

 dactylus, Dimorphodon, and Ramphorhynchus) ; and though 

 commencing in the Lias, they are most abundant in the Solen- 

 hofen Slate. The Dicynodonts appear to have died out ; but 

 the Deinosaurs are largely represented, chiefly by the genera 

 Megalosaurus and Cetiosaurus. 



The Birds have no other representative in the Oolitic period 

 than the extraordinary Archtzopteryx, macrura of the Solenhofen 

 Slates the first undoubted indication of birds in the geolo- 

 gical record. As has been before pointed out, this Jurassic 

 bird differed in several most important characters from all 

 known members of the class, whether living or extinct ; its 

 most striking peculiarity being the possession of a long, lizard- 

 like tail composed of free vertebrae, of which each supported a 

 pair of quill-feathers. 



The Mammals, taking all things into consideration, are well 

 represented in the Jurassic series, their remains belonging to 

 the two horizons of the Stonesfield Slate (Lower Oolites) and 

 the Purbeck beds (Upper Oolites). The Stonesfield Mammals 

 viz., Amphitherium, Amphilestes, Phascolotherium, and Stereog- 

 nathus are all of small size ; and the first three appear to be 

 certainly Marsupial. Stereognathus may be also a Marsupial, 

 but its true affinities are uncertain. The Purbeck Mammals 

 Triconodon, Spalacotherium, Galestes, and Plagiaulax were 

 likewise all of small size, and they appear to have been all 

 Marsupial ; the three first-named being probably insectivorous, 

 whilst the last appears to have been a vegetable-feeder. 



