7S2 TRANSACTIONS OF SECTION D. 



ou the coast is remarkable, such species often only remaining a few days. This is 

 particularly interesting to those of us wishing to avail ourselves of the short 

 opportunities we have of watching them. 



The paper was illustrated by a series of lantern-slides, and of skins of speci- 

 mens collected by the author, illustrating curious phases of plumage-changes, 

 according to sex, age, and season. 



ti. A Biological Sxpediiion to the Birket el Qiirun, Fayum Province of Egypt. 

 By W. A. CuNNiNQTON, B.A., Ph.D., andC. L. Boulenger, B.A. 



The lake known as the Birket el Qurun has a unique interest, since it is the 

 remains of the historic Lake Moeris, which was used as an artificial regulator 

 of the Nile floods by the monarchs of the twelfth dynasty. Our expedition was 

 undertaken in the spring of last year at the instigation of Captain Lyons, F.R.S., 

 the Director-General of the Egyptian Survey Department. 



While the Birket el Qurun is still of considerable size, being about twenty-five 

 miles long and having a maximum breadth of five or six miles, it is very evident 

 to the present-day observer that a remarkable reduction in size has taken place, 

 liaised beaches may be clearly recognised in many parts, and the lake is extremely 

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

 IS sufficiently brackish to be quite unpalatable, and its density is above that 

 of fresh water. It is thought that the surface of the lake was formerly as much 

 as 70 feet above sea-level; now it is some 140 feet below the level of the Medi- 

 terranean. 



The lake was found to be well stocked with forms of life, but apparently the 

 number of species is not large. With the tow-net there were taken large 

 quantities of Entomostraca — principally copepods and cladocera — as well as great 

 numbers of rotifers. Very little phyto-plaukton was obtained. 



The Entomostraca doubtless form the food-supply of the fishes, which occur in 

 astonishing abundance. Fifteen species of fish were obtained, belonging to seven 

 families. All are well-known Nile forms, but more than half were secured for the 

 first time by this expedition. A large specimen of the so-called Nile perch (Lates 

 iiiloticus) was examined, which measured 120 cm. and weighed 54 pounds. 



The swampy pools on the margin of the lake yielded ostracods, hydrachnids of 

 the genus FAilais, and five species of spiders. The moUusca belong to eleven 

 i^pecies, all of them being Nilotic forms. Among these mollusca only two species 

 of lamellibranchs are included. A small oligochc'Ete — Paranais liltoralig — is the 

 only aquatic worm obtained, as leeches and turbellaria appear to be absent. 



Our collection contained also a gymnolajmatous polyzoan, with a circular 

 ophophore and eight tentacles. Cordi/lophora was found growing in great 

 .'ibundance in the lake. Its occurrence is of considerable interest, since it has not 

 previously been recorded from Africa, and is not known to occur in the Nile, with 

 which the Birket el Qurun is in direct communication. The most interesting dis- 

 covery was that of a medusa and the associated hydroid stage. This form, which 

 has been named Mcerisia Lrjonsi, appears to bear a resemblance to the marine 

 genns, Sarsia. Whatever its exact ufiinities, it is difficult to account for its pre- 

 sence in the Birket el Qurun. 



The algfe and the truly aquatic higher plants were also collected. Among the 

 latter, specimens of Potamoyeton interruptus and Chara vulgaris are of interest, 

 since they show slight differences from the common forms. 



3. On the Distribution of Irish Freshwater Mites (Hydrarachuida). 



By J. N. Halbert. 



The author described the various stages in the life-history, and the importance 

 of the parasitic larval stage in the dispersal of the various species over large areas. 

 The geographical distribution of the species is very imperfectly known, but the 



