THE FIRST AIR-BREATHERS. 153 



that while related to this low type, they presented a much 

 greater range of organisation than it shows at present, evincing 

 a capability to fill most of the places now occupied by the 

 true reptiles. Some of them were aquatic, and with limbs 

 rudimentary or little developed, but many of them walked on 

 the land, and were powerful and predaceous creatures. They 

 had large and complex teeth, they were protected by external 

 bony plates, and some of them had in addition a beautiful 

 covering of bony plates and spines, and ornamental lappets. 

 Many had well-developed ribs, indicating a condition of respi- 

 ration much in advance of that in the ribless batrachians. 

 Some of them attained to size and strength rivalling those of 

 the modern alligators, while some of the smallest species 

 exhibit characters approaching in some respects to the lizards. 

 Perhaps the most fish-like of these animals are those first dis- 

 covered by von Dechen {Aj'c/iegosauriis, Fig. 134). Their long- 

 heads, short necks, supports for gills, feeble limbs and long 

 flat tail, show that they were aquatic creatures, presenting 

 many points of resemblance to the Ganoid fishes which must 

 have been their companions. Yet they show what no fish can 

 exhibit, fore and hind limbs with proper toes, and the complete 

 series of bones that appear in our own arms and legs, while 

 they must have had true lungs and breathed through nostrils. 

 So different are they from the fish in details, that a single limb 

 bone, a vertebra, a rib, or a fragment of a skull bone, suffices 

 to distinguish them. Much has been said recently of the 

 genesis of limbs ; and here, as far as now known, we have the 

 first true limbs ; but it is scarcely too much to say that the 

 feet of Archegosaurns differ more from the fins of any car- 

 boniferous fish than they do from the human hand ; while it is 

 certain that the feet which made the impressions represented 

 in Fig. 133, on the lowest beds of the Carboniferous, or fhat 

 from the upper coal-formation represented in Fig. 139, were 

 not less typical or perfectly formed feet than those of modern 

 lizards. 



