382 Messrs. Playfair and Letourneux on the 



speculations. It has been concluded that these fish inhabited 

 the vast subterranean sea which occupies the bottom of the 

 Saharan depression ; and it has been asked how, if they were 

 destined to live in perpetual obscurity, they were not destitute 

 of eyes like the Sirens of the grottoes of Carniola or the Crus- 

 tacea of the Mammoth Cave in the United States ? 



We have already noticed the existence, from Biskrah as far 

 as Temacin, of hahrs or gouffres, which communicate with the 

 underground sheet of water, and occupy too great a surface to 

 be regarded as the enlarged apertures of fallen-in wells. All 

 these apertures are inhabited by considerable numbers of Cy- 

 prinodons and Chromis. There they live freely, exposed to 

 air and light, and breed under normal conditions. Their 

 underground life is merely an episode, and as it were an inci- 

 dent in the voyages which they undertake between one hahr 

 and another. When they reach the neighbom-hood of a well, 

 they are either forced up with the water, or obey an instinct 

 to mount to the surface. 



It is less easy to explain the appearance of Barhus setifensts 

 in the basin of an artesian well near Miserguin (region of the 

 Tell), and of Cristiceps argentatus in the "rigoles d'dcoule- 

 ment " of the Fontaine Malakoff (in the region of the High 

 Plateaux) . The former fact is vouched for by the engineers 

 of the Fonts et Chaussdes, and the latter by the naturalist 

 Fanton. 



Do these barbel come by some concealed communication 

 from the subterranean depths into which the Tafna is engulfed 

 and in which it disappears during a part of its course ? The 

 fact is doubtful,, but by no means impossible. As to the Cris- 

 ticeps^ it appears to us probable that it may inhabit some of 

 the brackish springs at the foot of the mountains round the 

 basin of Zahrez, which doubtless communicate with the arte- 

 sian water-supply. 



If we examine the distribution of Algerian fish with refer- 

 ence to longitude, we observe that the richness of the fish- 

 fauna diminishes sensibly from east to west. The province of 

 Constantine possesses sixteen species, of which five are com- 

 mon to Algiers, Oran, and itself (namely, Mugil cephalus^ 

 Clupea finta^ Barhus callensis, B. setifensts, and Anguilla 

 vulgaris), and a sixth [Blennius vulgaris) common to Algiers 

 and Constantine; the other ten {Gohius rliodoj^terus, G.paga- 

 7iellus, Mugil capita, Salmo macrostigma, Leuciscus callensis, 

 Cyprinodon calaritanus, Syngnatlms algeriensis, Tellia apoda, 

 Chromis nilotica, and Ch. Tristrami) are not found in the 

 other provinces. 



This is easily explained by the extent of the zone of the 



