274 Transactions of the Society. 



The following is a description of the localities in which collec- 

 tions were made : — 



I. ALGERIA. 



Algiers. 



The neighbourhood of Algiers proved singularly barren. The 

 only pools in which anything living was found were some artificial 

 ponds in the Jardin d'Essai. These ponds are supplied with water 

 brought from the hills above the town, and are used for the culti- 

 vation of aquatic plants such as Papyrus. The following is a list 

 of the species found : — 



Asellus aquaticus Linn. 



Simosa vetula O.F.M. 



Ceriodaphnia reticulata Jur. 



Plcuroxus aduncus Jur. 



Chydorus sphtericus O.F.M. 



Cyclops albidus Jur. 



C. prasinus Fisch. 



C. bicuspidatus Claus. var. lubbocki Brady. 



C. strenuus Fisch. 



Biskra. 



The oasis of Biskra is the capital of the Central Zab district 

 of the Lower Sahara. It is situated on the very edge of the 

 desert, 124 m. above sea-level. The water supply of the oasis is 

 derived from two sources, the Eiver or Oued Biskra, and from 

 springs. The supply from the river is one of very fluctuating 

 quantity, and entirely ceases during the summer. In winter and 

 spring the whole river channel, which is some 400 yards wide, 

 may at times be filled by a turbid torrent, making it difficult to 

 realise that its waters at this point can fail entirely. The essential 

 source of water is therefore the springs, which rise in and by the 

 bed of the river itself, in several groups, 2£ kilometres to the 

 north of the town. Those of the left bank supply the oasis of 

 Filiach, while those of the right bank supply Biskra itself. The 

 water of these springs rises evidently from the cretaceous rocks of 

 the Atlas Mountains, and reaches the surface at a temperature of 

 29-33° C. (84-8° F.) and with about 2-16'grm. of dissolved salts 

 per litre ; it flows along the river bed, which would otherwise be 

 quite dry during the summer, and is directed by means of a low 

 masonry barrage into the main supply canal of Biskra. A large 

 part of the water is doubtless lost by percolation through the 

 gravel of the river bed, but the total volume available amounts to 

 about 10,000 litres a minute. One-tenth of the whole is taken by 

 a special canal for the needs of the town and garrison, the rest 



