BATRACII IA.
(Toads, Frogs, Newts.) Char.—Vertebne biconcave (Siren), proccelian (Rana), or opisthoccelian (Pips) : pleurapophyses short, straight. Two occipital condyles ; two vomerine bones, in most dentigerous : no scales or scutes. Larvae with gills, in most deciduous.
It is only in tertiary and post-tertiary strata that extinct species, referable to still existing genera or families of this order, have been found. The reptiles with amphibian or batrachian characters, of the carboniferous and triassic periods, combined those characters with others which gave them dis tinctions of ordinal value ; they illustrated, indeed, rather a retention of the more general cold-blooded vertebrate type, with concomitant piscine and saurian features, than any near affinity with the more specially modified naked or soft-skinned reptiles to which the name Batrachia is given in zoological catalogues of existing species.
Of the tailless or " anourous" Batrachia, toads of extinct species (Palcrophryiws Gessneri and P. dissimilis) have been discovered in the (Eningen beds ; and frogs, more abundantly, in both miocene and pliocene deposits of France and Germany. The batracholites from the tertiary lignites of the " Siehenge birge," near Bonn, show different stages of transformation of the Rana diluviana, Gdf. Tertiary shales from Bombay have made known to the author the small fossil Rana pusilla.
Of the salamander family, the most noted fossil is that which was referred, when first discovered at (Eningen in 1726, to the human species, as Homo diluvii testis. Cuvier demon strated its near affinities to the water-salamander (.ilenopoma) of the United States : more recently a living species of sala mander has been discovered in Japan which equals in size the fiissil in question—A ndrias Scheuchzeri.
A retrospect of the foregoing outline of the paheontology of the class of reptiles shows that, unlike that of fishes, it is now on the wane ; and that the period when Reptilia flourished under the greatest diversity of forms, with the highest grade of structure, and of the most colossal size, is the mezozoic. The progress of air-breathing vertebrates, graduating by close transitional steps from the water-breathing class, has been checked, as if it had been unequal to the exigencies and life capacities of the present state of the planet. Reptiles have been superseded by air-breathers of higher types, which cannot be directly derived from the class of fishes. A more general
ized vertebrate structure is illustrated, in the extinct reptiles, by the affinities to ganoid fishes shown by the Ganocephala, Labyrinthodontia, and Ichthyopterygia ; by the affinities of the Pterosauria to birds, and by the approximation of the Dino sauria to Mammals. It is manifested by the combination of modern crocodilian, cheloniau, and lacertian characters in the Cryptodontia and Dicynodontia ; and by the combined croco dilian and lacertian characters in the Thecodontia and Saurop tervia. Even the Chelonia of the Purbeck period illustrate the same principle, by the more typical number of modified hiemapophyses, or abdominal ribs, entering into the composition of their plastron.
The diagram (fig. 83) gives a concise view of the geological re lations, or distri bution in time, of the principal groups of the class Reptilia. In the column opposite the right hand, the dark mark shows that the ganoce phalous group re presented by the Arch egosaurus be gan, culminated, and ended in the carboniferous period. The Laby rinthodonts, cul minating in the trias, disappear at the base of the oolitic system. Of the true Batra ehia, those retain ing the tail appear to have been at their maximum during the upper tertiary period, and to have begun to decline after that time ; whilst the tailless genera and species are most numerous and various at the present day. The Ophidia resemble the Anoura, commencing in the older tertiary, and showing their maximum of development at the present day. The true proccelian, and especially the pleurodont, lizards, commencing a little earlier in the chalk, have also gone on increasing in number and variety of forms to the present day. The acrodont group was represented by Mosasaurus, with a maximum of size, during the cretaceous period. The Theco donts have but the partial relationship to modern Lacertilia which the Labyrinthodonts bear to the modern Batraehia. The great ordinal groups of Ichthyo- and Sauro-pterygia, of Pterosauria, and Dinosauria, together with the amphi- and opistho-ccelian Crocodilia, passed away ere the tertiary time had dawned. The proccelian crocodiles which culminated in the lower and middle tertiary times, are now on the wane, Perhaps, also, the same might be said of the Chelonia, in regard to the size of individuals and the number of species of certain genera (e. g. Cyclone, Trionyx, Chelydra).