BATRACHIAURODELA. 3 



we may have recourse. Thus, whatever be the number of fingers 

 and toes, they are always clawless in these Batrachians, for, the 

 geckos, which are amongst lizards those that might be mistaken for 

 them, although deficient in the development of their toes, will, never- 

 theless, always exhibit enough of these organs to guide the observer 

 without any difficulty. The absence of external auricular apertures, 

 is another feature peculiar to the tailed Batrachians, and but seldom 

 met with amongst lizards ; and, finally, the longitudinal anal aperture 

 is not the least amongst the distinguishing traits of these two divisions 

 of animals. 



The tailed Batrachians subdivide into two groups ; 



a. TREMATODEIRA, 



WHERE we observe either external or internal gills persisting through- 

 out life. When the gills are internal, there are branchial fissures 

 or apertures on the sides of the neck. 



SYN. Trlmatodlres, BUM. & BIBR. Erpet. gen. VIII, 1841, 53; &, IX, 1854, 174. 

 OBSERV. None of which were collected by the Expedition. 



/?. ATRETODEIRA. 



WHEN fully grown there are neither external nor internal gills, hence 

 no branchial apertures. The young, however, are provided with 

 external gills, which they gradually lose in growing up to maturity. 

 At this latter period of their existence, the lungs are called into 

 play, through the means of which they breathe the atmospheric air. 



Svy.Atrttodlres, BUM. & BIBR. Erpet. gen. VIII, 1841, 53; &, IX, 1854, 36. 



OBSERV. The species of Urodelian Batrachians collected by the 

 Expedition are but four in number, all of which belong to the second 

 group, that in which the gills and branchial apertures become oblite- 

 rated when entering upon the period of maturity, or full-grown state. 



These four species are distributed into four genera, one of which 

 belongs to the family of Salamandridae, and the three others to 

 that of Plethodontidae. 



