FAUNA OF THE OOLITES. 75 



drawings, of Medusae, which show that even at that time 

 this class had reached the state in which it still exists. 



The terrestrial fauna of the Jurassic period is like- 

 wise enriched by new forms and groups. We find the 

 first true crocodiles, tortoises, and the most remarkable 

 variation of the Sauroid type, the winged lizard or 

 Pterodactyl. It is evident from their well-preserved 

 skeletons that the wing membrane was stretched, as in 

 the bat, between the posterior and anterior extremities. 

 Behind, it extended to the foot, while in front, it obtained 

 a corresponding addition by the elongation of the little 

 finger. A first and only bird has likewise been found 

 in the well-known resting-places of the Pterodactyls, in 

 the lithographic slates of Solnhofen in Bavaria (Archse- 

 opterix lithographica). The most remarkable peculiarity 

 of this bird, recognizable by the most minute impression 

 of its feathers, is the long tail, bordered by two rows of 

 rigid feathers. The head is unfortunately crushed beyond 

 recognition. The inferior order of Mammals already 

 mentioned, the Marsupials, were also present, as is shown 

 by the enclosures of the middle Oolite of England and 

 the upper Oolite of the Purbeck strata. 



The ornithic animals of the chalk are more remark- 

 able intermediate forms than the Archaeopteryx, and 

 these by the hour-glass-shaped centres of the vertebrae 

 are directly connected with the sea-lizards of the Jura; 

 they also possess teeth ; this may, however, be the case 

 with the Archaeopteryx also. We shall return later to 

 these creatures, which fill up a void hitherto very con- 

 spicuous. During this new period the Ammonites were 

 most abundant, and then became extinct, after going 

 through a stage of degenerate forms which may be ob- 



