THE BATRACHIA OF NORTH AMERICA. 



251 



Classification. 



A. Ethmoid not ossified 



AA. Etlimoid ossified above: 

 1. A frontoparietal fon- 

 tanelle — 

 a. Prefrontals narrow.. 



aa. Prefrontals wide . . . 



]1. No fontanelle; skin 

 free; no exostosis — 

 a. Prefrontals narrow 



aa. Prefrontals wide 



111. No fontanelle; skin 

 free ; exostosis— 

 a. Prefrontals narrow.. 



aa. Prefrontals wide — 

 1111. No fontanelle; integu- 

 ment involved in 

 exostosis. 



11111. Skuli oxostosed, in- 

 volving integn- 

 iiieiit; temporal 

 fossa roofed 



mill. As last, but membra- 

 num tyrapani in- 

 closed behind 



Bufonidte. - 



Myobatra- 

 chus. 



Epidalea. .. 



Bnfo sp 



Biifo sp 



iPeltaphryne 

 >C ranoph- 

 S ryue. 



Otaspis . 



Scaphiopidaj. 



Didocus — 

 Spea 



Scaphiopus 

 Pelobates . . 



Cultripea 



Cystignathi- 

 cUb. 



Eusopbus . 



Borborocoe- 

 tes. 

 (Cyclorbam-1 

 ^. pbiis. ^ 

 'Hyperolia 



Elosia, etc . . 

 Hylodes, etc, 



Pbraetops . 



Calyptocepb 

 alus. 



Hvlidee. 



Thoropa ... 



Hypsiboas . 

 Hyla (sp.) . 



Scytopis . . . 



Osteocepba- 

 lus. 



Tracbyceph- 

 alus. 



EanidsB. 



Haniila. 



Rana (oxy- 

 rhyncha). 



Rana (hexa- 

 dactyla). 



Polypedates. 



Figures of tliese, and iiiterinediate types of crauia will be fouud ia 

 Plates GS to 75. 



The adaptive result attained by these changes in the cranial ossifica- 

 tion are two. Both in burrowing in the earth and in i»resenting a de- 

 fense against enemies, the top of the head is presented to the resisting 

 object. On being atacked, a Salieutian Batrachian always depresses 

 the muzzle and presents the top of the head to the enemy. The types 

 with well ossified crania have a great advantage over those iu which 

 the front is ineinl>ranous or cartilaginous, especially in the case of at- 

 tack from venomous snakes, stinging insects, etc. There is, however, 

 no definite distribution for the resi)ective types, either in time or space, 

 except that the genera with uuossitied ethmoid all belong to the South- 

 ern Hemisphere. Also, types with unossified frontoparietal bones pre- 

 dominate in the Australian and Neotropical realms, are unknown in 

 the Ethioi)ian, and rare in the Paleotropical. Types with exostosed 

 frontoparietals chiefly abound in the Neotropical realm, and occur 

 in the Nearctic and Palwarctic. Paleontologically, both exostosed 

 (Latonia) and membranous frontoparietals (Alytes) appear together iu 

 the Miocene brown-coal of Bonn, in Ehine-Prussia. 



As regards the distribution of Salientia in North America, the follow- 

 ing general remarks may be made. The oasteru district, with its com- 

 paratively humid climate and abundant- water courses, is the home of 

 the genus Eana. For similar climatic reasons the middle and northern 

 parts of the Pacific region have several species of Rana. The eastern 

 region, the land of forests, possesses nearly all the species of Hyla. The 

 Pacific coast has but one, a fact due, perhaps, to its long dry season . 



