474 



I, at least, am not able to point out any difference of the slightest 

 importance between European, Cis-Atlantean, and Trans-Atlantean 

 specimens in any single species. But, supposing there were persons 

 who had the hardiness to distinguish specifically these animals, what 

 other result would be gained for science than that of the existence 

 of two series of species (one north, the other south of the Medi- 

 terranean), so extremely similar, that, except from knowing the locality, 

 nobody could make them out ? No peculiarity in the feature of the 

 North African fauna would be expressed by it, and North Africa 

 would continue to belong zoologically, and not merely ornithologically, 

 to the Paleearctic Region. No other fact proves this so well as that 

 of the presence of Tailed Batrachians in these countries. 



If we ask for the boundary between the Faunas of the Palsearctic and 

 ^Ethiopian Regions, it is like the water-shed between the systems of two 

 rivers : tributaries of the one extend far within the reach of the other. 

 Nevertheless, we must draw such a line, and, the reptiles collected by 

 Mr. Tristram being identical with those north of the Atlas, it cannot 

 be found in the tract of those mountains, but it must be transferred 

 into the Desert itself*. Probably the iEthiopian fauna penetrates 

 into the Desert from the South, similarly as the European from the 

 North ; and some future attempt at a general account of the fauna 

 of the Sahara may be drawn up according to the three categories : — 



1. Animals generically and specifically belonging to the Palee- 

 arctic Fauna. 



2. Animals generically and specifically belonging to the ^Ethiopian 

 Fauna. 



3. Animals generically peculiar to the desert. 



The new genus of fishes described above appears to belong to the 

 latter category. It is remarkable from its habitat in ditches the 

 water of which is impregnated with the salt of the desert. The 

 fishes most closely allied to it live in the seas round the coasts of 

 Africa, viz. Chromis in the Mediterranean, Sarotherodon and Hemi- 

 chromis on the coast of Guinea, Glyphisodon in the tropical seas of 

 the west and east. To judge from the description, we find a similar 

 fish, though certainly different, perhaps a Chromis, indicated by 

 Lacepede (Hist. Nat. Poiss. iv. p. 161), with the name of Sparus des- 

 fontainii. It is said to be found in the warm springs of Cafsa near 

 Tunis, the water of which has a temperature of 30° R., and does not 

 contain mineral ingredients. He states further that the same species 

 is found in ordinary fresh water also at Tozzer. This would be not 

 improbable. The other fish, Cyprinodon dispar, found by Mr. 

 Tristram in the hot springs of Sidi Ohkbar, with a temperature of 

 80° F., and by Dr. Riippellt in those of Tor (27° R.), lives also 

 in ordinary fresh waters of the oases of Egypt, of Abyssinia, and 

 Syria :|:. This is a viviparous fish. 



* Cfr. Wallace in ' Ibis,' 1859, p. 449. 



t Riippell, Atlas Fische, p. 66 {Lebias dispar). 



I Cuv. et Val. xviii. p. 161 {Cyprinodon lunatus and moseas). 



