274 OBSERVATIONS ON THE RODENTIA. 



Family 2. Dactylethrida. Adult body short, frog-like. Tail none. Legs 

 four. Tongue distinct. Tympanum hid. 



Genera. — Dactylethra. Bombinator. Breviceps. 



Family 3. Astrodactylidce. Adult body short, flat, frog-like, tailless. Legs 

 four. Tongue wanting. Tympanum hid. 



Genus. — Astrodactylus. (Pipa). 



Family 4. Salamandridce. Adult body long, lizard-like. Tail long. — 



Legs four. 



Genera. — Salamandra. Salamandrina. Molge. Triton. 



Sub-class ll.—DIPLOPNEUMENA. Respiring doubly; both by lungs 



and gills. 



Order III. — Imperfectibranchia. Gills imperfect. 



Family 1. Menopomatidce. Body long, lizard-like; or lengthened, snake- 

 like; with a tail. Legs four. Gill-like organs internal. 

 Genera. — Menopoma. Amphiuma. 



Order IV. — Manentibranchia. Gills permanent. 



Family 1. Sirenidce. Body lengthened, snake-like, having a tail. Legs 

 two in front. Gills tufted, external. 



Genera. — Siren. Parvibranchus. 



Family 2. Proteidce. Body long, lizard-like, or fish-like, with a tail. Legs 

 four. Gills ramified, external. 



Genera. — Proteus. Menobranchus. Siredon. 

 (To be continued.) 



Art. III. — Observations on the Rodentia, with a view to point out 

 the groups as indicated by the structure of the Crania, in this Or- 

 der of Mammals. By G. R. Waterhouse, Esq., Curator to the 

 Zoological Society, Vice-Pres. of the Entomological Society. 



( Continued from page 188J 



Family IV. — MuridjE. 



Dentition. — Incisors compressed laterally: molars 44 S n 

 one genus -|4)> rooted ; the anterior molar of each series the 

 largest, and the posterior one the smallest. The series on 

 each side of each jaw widely separated and parallel. 



