CHAP. xix.J KEPTILES. 385 



the Nearctic is actually richer than the Neotropical region both 

 in genera and species. This would point to the conclusion, that 

 the group originated in the Indo-Chinese sub-region and spread 

 thence north-east to North America, and so onward to South 

 America, which, having been the last to receive the group, has not 

 had time to develop it largely, notwithstanding its extreme 

 adaptability to Eeptilian life. The genera are divided among 

 the several regions as follows : 



Craspedocephalus (7 sp.), Tropical America and the West In- 

 dian Islands ; Cenchris, Crotalophoms, Uropsophorus, and Crotalus, 

 inhabiting North America from Canada and British Columbia 

 to Texas, one species (Crotalus horridus) extending into South 

 America; Trimeresurus (16 sp.), all India from Ceylon to Assam, 

 Formosa, the Philippines, and Celebes ; Peltopelor and Hypnale 

 (1 sp. each), peculiar to India ; Calloselasma (1 sp.), Siam ; 

 Atropos (1 sp.), Java and Borneo ; Halys (3 sp.), peculiar to 

 Tartary, Thibet, Japan, North China, and Formosa. 



FAMILY 25. VIPEKID^E. (3 Genera, 22 Species.) 

 GENERAL DISTRIBUTION. 



NEOTROPICAL I NEAKCTIC 

 SUB-REGIONS. SUB-REGIONS. 



PAL^EARCTIC I ETHIOPIAN I ORIENTAL I AUSTRALIAN 

 SUB-HEGIONS. SUB-REGIONS. SUB-REGIONS. SUB-REGIONS, 



1 . 2 . 3 . 4 1 . 2 . 3 . 4 1.2.3.4 



The Viperidse, or True Vipers, are especially characteristic of 

 the Palsearctic and Ethiopian regions, only one species being 

 found over a large part of the Oriental region, and another 

 reaching Central India. They are especially abundant in Africa, 

 and the Palsearctic confines in South-western Asia. The 

 common Viper ranges across the whole Palsearctic region from 

 Portugal to Saghalien Island, Beaching to 67 North Latitude, in 

 Scandinavia, and to 58 in Central Siberia. The genera, accord- 

 ing to Dr. Strauch's synopsis, are distributed as follows : 



Vipera (17 sp.), which has the range of the family, extending 

 over the whole of the Palsearctic and Ethiopian regions, except 

 Madagascar, and as far as Ceylon, Siam, and Java, in the Oriental 



