4 ON AN EXPEDITION TO THE BIKKET-EL-QURUN. [Jail. 14, 



signs of a considerable reduction in size, for raised beaches are in 

 many places very apparent, and the lake has become extremely 

 shallow, the greatest depth being between four and five fathoms. 

 Additional evidence is afibrded by the nature of the water, which 

 is sufficiently brackish to be quite unpalatable. The density is 

 .slightly above that of fresh-water, and the proportion of soluble 

 salts about one-fourth that in the ocean. 



The almost complete absence of seiche alterations of watei--level 

 is probably due to the shallowness of the lake, as are also the 

 rather striking figures obtained of the water temperature. A 

 maximum of 94'2° was observed in very shallow water close to 

 shore about 2.0 p.m., whilst a minimum of 54-8° was obtained as 

 a surface reading in the early morning. The difierence between 

 the surface temperature and that of the water below may also 

 be very great, one reading showing the water at three fathoms to 

 be 12-4° colder than that at the surface, whilst a difierence of 8-8° 

 was detected in water only one fathom below. 



The lake would seem to be remarkable more for the quantity of 

 life which its waters contain, than for the number of different 

 species inhabiting it. From the greenish water, the tow-net 

 collects immense swarms of Entomostraca — principally Copepoda 

 and Oladocera — as well as large numbers of Rotifera. The only 

 phyto-plankton, however, which is present in the tow-nettings, 

 consists of two or three species of Diatoms. 



The fish collected by the expedition were obtained for the most 

 part from the native fishermen, who secure large quantities from 

 the well-stocked waters. The fishing industry is highly organised 

 and the bulk of the catch is despatched to the Cairo market. 

 Fifteen species of fish were secured, belonging to seven families. 

 All of these are well-known Nile forms, but more than half of 

 them are recorded for the first time from the Birket-el-Qurun. 

 The so-called Nile perch {Lates niloticus) is stated to attain a large 

 size in the lake, a specimen which measured 1 20 cm. and weighed 

 54 lbs. being considered by the local people as by no means 

 •extreme. Although 15 species are thus known to inhabit the 

 waters of the lake, two of them occur in such remarkable 

 abundance as to make the others appear rare. These are Tilajna 

 galilcea and Tilapia nilotica, the latter being the more abundant. 

 The fish markets very frequently contain nothing but these two 

 species, which are caught with casting nets in the swampy 

 shallows, or with seines in the deeper water. 



In addition to Copepods and Oladocera from the open lake, 

 'Ostracods are found on the muddy bottom and in the swamps, 

 while certain Oniscidte were collected on the beach. It is rather 

 singular that no other Crustaceans were obtained : no crabs or 

 prawns were procured, although they are well-known in the Nile, 

 neither were any Argulidte observed on the large numbers of fish 

 examined. In the swampy pools on the lake margin were found 

 water-beetles of apparently little interest, Hydrachnids of the 

 genus Eulais, and certain spiders. . 



