NATURAL SCIENCES OF PHILADELPHIA. 299 



Silurians (the Acrodonta) abounds in the Ethiopian and Australian regions; 

 they are as abundant in the Indian and Palaearctic regions of the Northern 

 Hemisphere. In the Southern also, by Uromastix and the Rhynocephalia, 

 they approach nearest the ancient types of the Dicynodontia and the Croco- 

 dilia. Lacertidse, and not Teidae, occur in the ^Ethiopian, but they are but a 

 proportion of the whole, which chiefly exists in the Nearctic. 



Raniforni and not Arciferous Anura populate South Africa; they, however, 

 form but a small proportion compared with the great series of the Nearctic, 

 Palaearctic and Palreotropical regions. It is, however, superior in Anura to 

 the Nearctic, taken by itself. 



Rasorial birds and not Pullastras are the food species of South Africa ; but 

 they do not compare in abundance or size with those of the three regions just 

 mentioned. 



Moreover, but few Clamatores exist in either Australia or ^Ethiopia. The 

 Oscinc types are abundant, nevertheless they cannot be compared in abundance 

 with those of the northern regions. It must also be remembered that the mi- 

 gratory capabilities of birds render them less expressive of the true nature of 

 any fauna. 



The higher family of the Quadrumana, the Simiidae, replaces in Africa the 

 CebidjB of the Neotropical ; they are, however, most abundant in the Palaeo- 

 tropical region, in the other hemisphere. 



There are two ancient or inferior types of the Northern Hemisphere: first, 

 its Ganoid fishes, the Sturgeons of the Nearctic and Pala?arctic, and the Gars 

 of the Nearctic. The latter only have representatives in the Southern Hemi- 

 sphere, Polypterus and Calamoichthys in Africa, and so may be said to be 

 equally distributed ; but the former are confined to the north. We do not 

 know, however, whether they are of a modern or an ancient type, nor do we 

 know of extinct sturgeons in the Southern Hemisphere. Indeed, the Ganoid 

 series is not well defined or known as yet. If, as Agassiz states, the Siluroids 

 pertain to it, it is cosmopolitan, though least represented in the Pahearctic. 



Second, the Tailed or Urodele Batrachia. This order, entirely characteristic 

 of the Northern Hemisphere, is a group which combines characters of Anura 

 with those of the ancient forms, and possesses in its Nearctic types many of 

 low development. The Gj'mnophidia of the Southern Hemisphere cannot be 

 considered inferior to them. In the possession of this group the Northern 

 Hemisphere presents its first element of inferiority. 



The preceding comparisons indicate also the relations of the regions proper 

 to each other. It is obvious enough that the ^Ethiopian is much superior 

 to the two others of the Southern Hemisphere. As to the Australian and Neo- 

 tropical, the former must still be regarded as probably the most ancient, though 

 possessing at the same time a much stronger admixture of northern forms. I 

 have already presented the relations, with the inferior forms of each, thus :* 



R. A us trails. — Inferior in Monotrematous and Marsupial Mammalia, Pul- 

 lastriform and Struthious Birds, Serpentiform Pleurodont Lacertilia, 

 Arciferous Batrachia, Pleurodire Tortoises, its Elapid venomous snakes, 

 and the -whole Flora, according to Unger. 



R. Neotropica . — Marsupial and Edentate Mammalia, Inferior Rodentia and 

 Quadrumana, Pleurodire Tortoises, Pleurodont Lacertilia, Arciferous Ba- 

 trachia, Clamatorial and Pullastriforra Birds, Characin and Erythrinid 

 Malacopterigii. 



Cojiclusions. 



The following maybe looked upon as conclusions which have been indicated 

 in the preceding pages : 



I. Species have developed from preexistent species by an inherent tendency 



* Journ. Acad. Nat. Sci. Philada. 18G6, 109. 



1868.] 



