lOO PROCEEDINGS OF THE GEOLOGICAL SOCIKTY. 



continent, the biological evidence may be accounted for without the 

 necessity for land-communication. Singularly enough, so far as our 

 present information as to the depth of the southern oceans goes, 

 there would appear at first sight to be less difficulty in supposing a 

 former extension of the southern continent to xiustralia and South 

 America than to Africa, the depth as shown on the ' Challenger ' 

 chart south of the former continents nowhere exceeding 2000 

 fathoms, whereas to the south of Africa there is represented a con- 

 siderable belt of greater depth. But on an Admiralty chart, for 

 which I am indebted to Captain Wharton, R.N., P.H.S., and on 

 which all the known deep soundings are marked, none are shown south 

 of the southern extremity of Africa ; and it is clear that, in this 

 and other regions, more soundings are required before the contours 

 of the sea-bottom in the oceanic area can be considered as deter- 

 mined with accuracy. So far as our present information goes, the 

 ocean south of the Cape of Good Hope may bo no deeper than the 

 Mozambique Channel, though probably the depth is greater in the 

 former case. 



The faunal relations between Africa and South America are very 

 different from those between the latter and Australia. Here, again, 

 there are marked cases of affinity between the freshwater fishes, the 

 two important families Chromididce and Characinidcehemg (with the 

 exception of the few Asiatic Chromididce already mentioned) confined 

 to the two continental areas. ]N"or is this all, for in the Characi- 

 nidce, a large and important family, three out of the eleven sub- 

 families into which the family is divided by Giinther are both 

 Ethiopian and Neotropical. The importance of this fact is so great 

 that it deserves particular attention, for it proves a very large 

 amount of communication between the two areas, it being manifest 

 that members of all three subfamilies were transferred from one to 

 the other continent after extensive differentiation had taken place 

 in the family. 



Again in the Siluridce, two subfamilies are confined to the same 

 two regions, and amongst the few living representatives of Dipnoans, 

 two closely allied genera, Lepidosiren and Protopteriis, represent each 

 other, the former ih South America, the latter in Africa. 



In the reptiles the principal noteworthy cases of relationship are 

 the following : — The Chelonian family PdZowiecZwsn/ce comprises three 

 genera, all found in Madagascar ; two are also met with in Africa, but 

 not in South America, whilst one genus, Podocnemis, is also South 

 American, but not African. The Laccrtilian family Amphishamidce 



