ERSE

Another order oi Reptilia is clearly indicated by the remains of several large or even gigantic species now extinct, in which the extremities were modified to serve as fins on the plan of the paddles of the Cetacca, These reptiles are chiefly referable to the genera Ichthyosaurus and Plesiosaur us i they were marine, and of predaceous habits, and constitute the order Enaliosauria. The Chelonia form a third and very natural order. Those Saurians of Cuvier which have a heart composed of a single ventricle and two auricles, which have a bifid tongue and double intromittent organ, and Avhich have a scaly and generally imbricated covering, form a fourth order of reptiles, to which the term Squamata has been given. The Ophidia of Cuvier constitute the fifth order of reptiles. Some naturalists have proposed to unite the serpents with the lizards in the same order, on account of the gradual transition traceable in different genera from one to the other group; but the cla of reptiles, by parity of reasoning, ought to be merged in that of fishes; and the naturalists who favour the blending of the tetra podal with the apodal reptiles seem to forget that an order is a conventional division, a group of convenience, and not an entity circumscribed by nature. To separate the Batrachia as a distinct cla from the Reptilia, seems to be an error in the opposite extreme. The viviparous four-footed salamander, breathing air by membranous lungs, and circulating blood by a biauricular heart, is thus placed in a distinct cla from the four-footed lizard, without any e ential difference in the pulmonary or sanguiferous systems to warrant the separation; the only differences that can be urged for such a step are a modification of the tegumentary covering, and a greater development and later continuance of the temporary branchial apparatus, of which traces are met with in the embryos of all the air-breathing Vertebrata; and a modification of the reproductive system. The naked integument; the presence of external gills in the young state; the almost simultaneous fecundation, sometimes without intromi ion, of numerous ova, — may be grounds for regarding the Batrachia or Amphibia as a subcla , or a group somewhat higher than an order; but seem not to warrant their separation from the scaled reptiles as a distinct cla , as a group equivalent among Vertebrata to that of birds or mammals. For the subdivisions of the above orders see Lcuugata, Enaijo-sauuia, Chelonia, Squamata, Ophidia, Batrachia, and alsQ Amphibia. [s. 428]