ScHAHFF — Some liemarks on (he Atlantic Problem. 2S;} 



KuKjl being known from Southern Brazil, Uruguay, and Argentina, 

 while the allied A. africanus is only met with in West Africa. 



Among the snakes, we find similar cases of distribution. Thus 

 the Boina3 are mostly South American, but one genus Eryx inhabits 

 North Africa, Greece, and south-western Asia. The genus Boa is 

 conjSined to Central and South America, with the exception of the 

 two species B. Damerili, and B. madagmcariensis^ which turn up far 

 away in Madagascar. This curious relationship between Madagascar 

 and South America, which occurs among many groups of animals, 

 has already been alluded to. 



There are naturalists who attribute such cases to " convergence," 

 in order to obviate the difficulties of land-connections across deep 

 oceans ; but I cannot see how the two species of Boa, agreeing in 

 every anatomical detail with the characters peculiar to the American 

 genus, could have arisen independently in Madagascar. The Boidse, 

 too, must be looked upon as a comparatively ancient family ; though 

 the Ophidia, as a Avhole, are no doubt a relatively young branch of 

 Eeptiles, and, according to Dr. Gadow, essentially of Tertiary date 

 (p. 586). 



This theory of convergence, so much discussed at present, appears 

 to me even less applicable to fresh-water than to land forms. Yet 

 among the Pelomedusidse, a family of fresh-water tortoises, a species 

 of Podocnemis occurs in Madagascar ; while several allied species of 

 the same genus are commonly met with in South America. 



Amphibians. 



Whether Rana esculenta, the common edible frog of the Canary 

 Islands and the Azores, is indigenous or not will probably never 

 be known, as we cannot altogether rely on the reports of its sup- 

 posed introduction. To the latter islands, it is said to have been 

 brought in the beginning of the last century ; while the introduction 

 to the Canary Islands dates, according to Steindachncr, from the 

 sixteenth century. 



Besides the common frog, the tree frog {Uyla arhorca) inhabits 

 most of the islands of the Canarian archipelago, and also Madeira and 

 the Salvages, 



The distribution of the genus Hi/la is very instructive, as it is 

 almost entirely confined to America and Australia. It is absent 

 from the Ethiopian llegion, and only represented by a few species in 

 Europe and Asia. It has probably come to us from the East, spreading 

 chiefly along the Mediteiranean, where it lias formed several distinct 



