336 henry b. ward: 



Garda certainly not of a relict character but introduced pas- 

 sively from northern freshwater bodies. 



The presence of a fauna relicta in African lakes has received 

 strong confirmation in the recent investigations of Moore on 

 Lake Tanganyika. This water basin contains a medusa, six 

 quasi-marine gastropods, two prawns, one crab and several pro- 

 tozoa, all marine in character and together constituting what 

 the author calls a halolimnic fauna. These geographically 

 isolated forms can not have made their way up the stream 

 flowing from the lake, in fact only one occurs on that shore 

 where the outlet empties into the sea; they cannot have been 

 carried overland, being deep water forms in part at least; they 

 are not like modern oceanic forms, but are similar to Jurassic 

 types. The common freshwater fauna was marked in geologic 

 deposits of that period, hence it originated previous to these 

 halolimnic forms which arc consequently evidence of the 

 contamination of the lake by a deep arm of the sea in wjiat is 

 geologically speaking no very remote period of time. 



Giinther (94), speaking of the relict forms in Africa, notes 

 thai the freshening of the water must have come very grad- 

 ually since- evaporation is so rapid in the tropics. Rizzardi 

 (94) finds in a small crater lake B considerable fauna relicta 

 and concludes that this demonstrates the marine origin of the 

 water basin. In discussing another lake (iarbini (93) had pre- 

 viously shown that such a fauna may owe its origin to passive 

 introduction. Iloernes (97) states still more sharply the argu- 

 ment in the case of Lake Baikal; a relict fauna does not neces- 

 sarily demonstrate the relict character of the water basin. The 

 former may have come, as in Lake Baikal, indirectly from the 

 marine source through other bodies of water, no longer in ex- 

 istence; and the connection was in this case more probably with 

 the Mediterranean than with the northern ocean. 



