278 Transactions of the Society. 



the same distance from Oumach, which lies to the south of Biskra. 

 There are three springs, differing somewhat from each other in 

 nature. The first, which is called Ain-el-Hadjar, springs from a 

 hole in the base of a mass of limestone rock, and has an output of 

 about 1800 litres a minute at a temperature of 26° C. according to 

 my own observation. The water is very clear, rather sulphurous 

 to the taste, but of normal density. The bed of the outflowing 

 stream is covered with small stones, under which were found 

 swarms of Gammarus simoni, and, at the mouth of the spring, a 

 few specimens of a Cirolana which I have described as Cirolana 

 foutis. Another spring, or group of springs, known as Ain-el- 

 Faouar, are apparently of similar origin to the Ain-el-Hadjar. 

 The third group, named Ain Moglonb, lies a little to the east. 

 H>re there are two large springs having the form of more or less 

 round pools, the one about 4 metres across, the other smaller, and 

 both very deep and clear. The bottom is all shifting sand, and 

 there is a sort of film of white which ever and again spreads over 

 the bottom of the pool and draws back again. The spring is inter- 

 mittent, now bubbling furiously and now sinking quiescent, but with 

 no regular periodicity comparable to that of geysers or the so-called 

 tidal wells of Australia and other places. An Arab assured me 

 that the water comes from the sea ; but, however that may be, it 

 is here cp^ite fresh and drinkable, with a temperature of 26*33° C. 

 In the outflow from this group several specimens of Paltvmonetcs 

 varians were found. The water from all the springs is collected 

 into an artificially embanked channel which leads straight over 

 the desert to Oumach. In this channel Potamon fluriatilis and 

 Parous callensis abound, while Tilajiia zillei was found in the 

 Ain Mogloub and in the outflow of Ain-el-Hadjar. Paltvmonetes 

 varians probably occurs sparingly throughout the length of the 

 channel, as it was found, in the first instance, by Lord Walsingham 

 about five kilometres from the springs. 



II. TUNISIA. 



OUED TlNDJA. 



Oued Tindja station is about thirty miles north-west of Tunis, 

 betwen the lakes of Garaa Achkel and Bizerta. Garaa Achkel is 

 a great lake surrounded by hills on three sides and with a barren 

 sandy shore. At the time of my visit the water was fresh to 

 the taste and to the salinometer, and was at an unusually high 

 level. It was said to have been 3 metres above its usual level a 

 short time before, but was then falling. We were told that during 

 winter and spring this lake contains fresh water and has an outflow 

 into Lake Bizerta, but that, during summer, owing to evaporation, 



