166 THE GENESIS OF SPECIES. [CHAP. 



connexion between Africa and India, harmonizing with 

 what we learn from Miocene mammalian remains. 



On the other hand, the Characinidse (a family of the 

 physostomous fishes) are found in Africa and South Ame- 

 rica, and not in India ; and even the component groups of 

 the family are so distributed, namely, the Tetragonop- 

 Jerina 1 and the Hydrocyonina.- 



Agaiu, we have similar phenomena in that almost ex- 

 clusively fresh-water group the Siluroids. 



Thus the genera Clarias 3 and Heterdbranchus 4 are found 

 both in Africa and the East Indies. Plotosus is found in 

 Africa, India, and Australia, and the species P. anguillaris 5 

 has been brought from both China and Moreton Bay. 

 Here, therefore, we have the same species in two distinct 

 geographical regions. It is however a coast fish, which, 

 though entering rivers, yet lives in the sea. 



Eutropius^ is an African genus, but E. obtmirostris 

 comes from India. On the other hand, Amiurus is a North 

 American form ; but one species, A. cantonensis, 7 comes 

 from China. 



The genus Gfalaxias 8 has at least one species common 

 to New Zealand and South America, and one common to 

 South America and Tasmania. In this genus we thus have 

 an absolutely and completely fresh- water form of the very 

 same species distributed between different and distinct 

 geographical regions. 



Of the lower fishes, a lamprey, Mordacia mordax, 9 is 

 common to South Australia and Chile ; while another form 



i See Catalogue, vol. v. p. 311. 2 Ibid. p. 345. 



3 Ibid. p. 13. 4 L Ibid. p. 21. 5 Ibid. p. 24. 



6 Ibid. p. 52. ?L Ibid. p. 100. 8 Ibid. vol. vi. p. 208. 



9 Ibid. vol. viii. p. 507. 



