The batrachia of north America. 395 



rope eastwards to the Sierra I^evada or to the Rocky Mouutains. In 

 this genus is repeated the phenomenon observable elsewhere, that 

 the species of the Atlantic Coagt region are more different from those 

 of the Old World than are those of the Pacific coast. 



The longitudinal dorsal ridges constitute a peculiar feature not found 

 in any of the other genera of Batrachia Salientia of the United States. 

 They exist in most of the species, with the exception of R. catesbiana 

 and B. montezumae. Sometimes the skin above is perfectly smooth, 

 sometimes roughened by tubercles ; the same species will occasionally 

 present both extremes under different circumstances. The vocal sacs- 

 one on each side of the throat — are, when inflated, visible externally 

 in R. virescens, areolata, and montezmnce; possibly in others. The 

 amount of webbing between the toes varies from the fullest condition 

 in B. catesbiana, septentrionalis, and boylii, to the half webbing of E. 

 areolata. 



The distinctive characters of the species are derived from the com- 

 parative bulk of the body or limbs ; the presence or absence of dorsal 

 ridges ; the comparative length of fore arm and hand ; of femur, tibia, 

 foot, and body ; the amount of webbing between the toes j the compara- 

 tive length of the third and fifth toes (the fourth being always longest); 

 the shape of the tongue; the position of the vomerine teeth ; the size of 

 eye and tympanum, etc. The colors may present dark blotches, areo- 

 lated or not, reticulations or marmorations on a light ground, or light 

 sinuations or spots on a dark ground. Many species have a light line 

 along the jaw, which begins distinctly either at the nostrils or under 

 the eye. Those in which this line is wanting are R. catesbiana, montezumce, 

 areolata, septentrionalis, boylii, and some varieties of clamata. Speci 

 mens vary much, even of the same species, with latitude and external cir- 

 cumstances. As a general rule, those from the north are larger, darker, 

 and more pustular, so much so, that for i^. catesbiana, pahcstris, oirescens, 

 and clamata it is quite easy to establish two or three different races, 

 some of them even raised to the rank of distinct species. As, however, 

 all intermediate stages may be detected on a close examination of many 

 specimens from the same locality, although a general adherence to the 

 type is preserved, it becomes impossible to assent to the retention of 

 several long-established species. 



The following tabular analysis gives in a synoptical form the most 

 salient features of the different species. It is, however, impossible here, 

 as elsewhere, to indicate characters which shall apply with mathemat- 

 ical accuracy to all specimens of the same species. The dimensions, 

 proportions, color, and other characters may vary to a considerable ex- 

 tent, and it is only by striking the balance of all the features of a spe- 

 cies that we can determine its true position. 



