THE SCOUTS OF THE REPTILE HORDE. 167 



ion that those sandstones are older than the Carboniferous 

 Age, or even older than the Trias. Besides these, the most 

 ancient traces of reptilian remains occur in the coal-meas- 

 ures, which were deposited during the decline of the empire 

 of fishes in the latter part of the Carboniferous Age. 



The geological history of reptiles possesses many points 

 of extreme interest ; and, in order to make them clear to 

 the reader, and to give precision to the brief account which 

 I am about to furnish, I shall endeavor to recall in few 

 words the classification of this group of vertebrates. 



Reptiles proper, in point of rank, are next above the 

 Batrachians, which come next above the Fishes. Reptiles 

 are purely aerial in their respiration; Fishes purely aquatic ; 

 while the Batrachians breathe water in infancy, and air at 

 maturity, exhibiting thus a compromise between the ich- 

 thyic and reptilian modes of respiration. The body of the 

 reptile is always covered with scales or bony plates, while 

 that of all modern batrachians is smooth or " naked." The 

 vertebrae of most reptiles are concave at one extremity — ■ 

 generally the anterior — and convex at the other ; the ver- 

 tebrae of batrachians are concave at both extremities, like 

 those of fishes. There are other distinctions to which I 

 need not refer. The frog is the type of the highest order 

 of existing batrachians, the salamander of the second, and 

 the " fish-lizard" of the lowest. - The first is possessed of a 

 tail only in the young or tadpole state ; the second retains 

 its tail during life ; and the third retains both its tail and 

 aquatic — or embryonic — mode of respiration. 



Of reptiles, three orders which have played a most con- 

 spicuous and important role in the history of the world are 

 entirely extinct, and three others still survive. The tur- 

 tles, saurians, and serpents, in descending order, embrace 

 existing reptiles. The first are inclosed in a carapace or 

 " shell ;" the second have elongated forms, generally clothed 



