310 GEOGRAPHICAL AND GEOLOGICAL DISTEIBUTIOK. 



found by Tschudi in the Peruvian Andes at an elevation of nearly 

 16,000 feet. Among the more distinctive forms of Cystignathidae 

 are the horned frogs (Ceratophrys), which inhabit tropical America 

 from Guiana to Uruguay. 



A remarkable instance of a divided family among the Anura is 

 furnished by the Dendrobatidae, which comprise two genera and 

 ten species, one genus, Mantella, being confined to Madagascar and 

 Nossi B6, and the other, Dendrobates, to tropical South America. 

 The intermediate tracts are entirely devoid of representatives of the 

 family. The number of families restricted to a single zoogeographi- 

 cal region is five, of which four characterise the Neotropical realm 

 — Dendrophryniscidse, Amphignathodontidae, Hemiphractidse, and 

 Pipidae — and one, the Dactylethridae, the Ethiopian. The most 

 limited of all the families is the Pipidae, which is restricted to a 

 single species, the Surinam toad (Pipa Americana), an inhabitant 

 of Guiana and Brazil. 



Of the four primary groups to which the animals of this class 

 are referable, the Stegocephala (corresponding to the Labyrintho- 

 dontia of most authors), Gymnophiona (ccecilians), Urodela (sala- 

 manders, tritons), and Anura (frogs and toads), the first acquires 

 special geological importance from the fact that all, or very nearly 

 all, of the older forms are comprised within it. Remains of Urodela 

 are only doubtfully known from the Paleozoic deposits, while the 

 anurous type does not appear before the Tertiary epoch; no fossil 

 ccecilian has as yet been discovered. 



The now wholly extinct order Stegocephala, which comprises 

 salamandroid and ophidian forms more or less covered with a pro- 

 tecting armour of bony (ganoid) plates, dates from the Carbon- 

 iferous period (Hylerpeton, Batrachiderpeton, Pelion, Dolichosoma, 

 Ophidei-peton), when, or at a still considerably earlier era, they 

 appear to have become differentiated from the type of lung-fishes 

 (Dipnoi) or of the dipteroid ganoids. . A further development of 

 types, with a partial persistence of Carboniferous genera, is mani- 

 fest in the Permian deposits, where, as in the older strata, the 

 forms are principally referable to the division Ganocephala (Archse- 

 gosaurus, Dendrerpeton, Branchiosaurus, Protriton,* Hylonomus, 



* Protriton Petrolei is. by Scicbmuller considered to bo identical with 

 Brancbiosaui-us gracilis. 



