196 REPOUT~1841. 



tiles and Fishes, in regard to the great proportion of genera which are com- 

 mon to the Wcaklen and Oolite, and the small proportion which is continued 

 into the Cretaceous formations, offers a valuable corroboration of the subordi- 

 nate character of the Wealden group as a member of the great Oolitic series. 



No species or genus of Saurian represented by fossils from the Oolite has 

 yet been discovered in older or lower strata in the British Islands. The Rys- 

 osteus is apparently confined to the bone-bed under the lias, which may be 

 regarded as the oldest member of the Oolitic series in these islands. 



The Reptiles of the Poikilltic strata exhibit deviations from the typical 

 structure of the recent families, together with osculant characters joining 

 groups now distinct, as great and even more anomalous than occur in any of 

 the preceding extinct genera. 



The Rhynchosaurus of the New Red Sandstone near Shrewsbury manifests 

 Ornithic and Chelonian modifications, grafted upon an essentially Lacertian 

 type of cranial structure ; no approach even to the form of its extraordinary 

 head being made by any other of the extinct members of the Saurian order. 

 The vertebrae of the Rhynchosaurus differ from those of existing Lizards, 

 Chelonians, and Birds, and combine the biconcave structure with the oblique 

 processes and costal articulations of the vertebrae of recent Lizards. 



The -Labyrinthodonts of the same formation exhibit a different but an 

 equally remarkable combination of characters, Crocodilian modifications being 

 superinduced upon a fundamental organization of the Batrachian type. The 

 structure of the teeth in this remarkable family, which is the most complex 

 that has hitherto been met with in the whole animal kingdom, is unique in 

 the class of Reptiles, and is but partially and comparatively feebly repeated 

 in that of Fishes. It is highly probable that the modifications of the loco- 

 motive extremities were as peculiar as the dental characters, if we may judge 

 from the foot-prints of the so-called Chdrotherium, to which the Labyrintho- 

 donts alone have at present an equitable claim. 



Finally, tlie Palceosaurus and other genera of the Magnesian conglome- 

 rate, like the so-called Monitors of Thuringia, are lizards which combined a 

 thecodont type of dentition, with biconcave vertebrae, having the superadded 

 peculiarity of a series of ventricose excavations in the bodies of the vertebrae 

 for the spinal chord, instead of a cylindrical canal. 



Below the New Red Sandstone system, notwithstanding that the older de- 

 posits, as the coal-measures, have been more thoroughly explored by man than 

 any other geological formation, no trace of a vertebrate animal more highly 

 organized than a fish, has been detected. 



From this survey it is evident that many races of extinct reptiles have suc- 

 ceeded each other as inhabitants of the portion of the earth now forming 

 Great Britain ; their abundant remains, through strata of immense thickness, 

 show that they existed in great numbers, and probably for many successive 

 generations. Their coprolites prove that they fed upon organized beings co- 

 existing with them and characterizing the same strata, but now equally ex- 

 tinct with their devourers. 



To what natural or secondary cause, it may then be asked, can the succes- 

 sive genera and species of Reptiles be attributed ? Does the hypothesis of 

 the transmutation of species, by a march of development occasioning a pro- 

 gressive ascent in the organic scale, afford any explanation of these surprising 

 phenomena? Do the speculations of Maillet, Lamarck and Geoffroy de- 

 rive any support or meet with additional disproof from the facts already 

 determined in the reptilian department of Palaeontology ? 



A slight survey of organic remains may, indeed, appear to support their 



