358 CHARLES L. BOULENGER. 
but except during high Nile receives very little water. 
There is no outlet, the waters of the lake are therefore 
decidedly brackish. A general summary of the results of 
our investigations was published in a letter to ‘Nature’ last 
August. With the exception of the Hydromedusan which 
forms the subject of this paper, of Cordylophora, and of a 
ctenostomatous Polyzoan, resembling Victorella, which 
occurs in great abundance, the fauna seems essentially a 
freshwater one, composed probably of such inhabitants of 
the Nile as can accommodate themselves to the salinity of 
the water. 
The hydroid stage of Mcoerisia was obtained for the first 
time at the beginning of April. As medusa-buds were present — 
on the hydranths we carefully watched for free-swimming 
medusz ; these, however, did not appear in our tow-nettings 
until May, when they first began to swarm. 
Both stages were exhibited by me at the meeting of the 
Zoological Society of London held on June 18th, 1907, when 
the name Meerisia lyonsi, gen. and spec. nn., was pro- 
posed for this new form. 
I desire to take this opportunity to express our sense of 
deep gratitude to Captain H. G. Lyons, F.R.S., and his 
assistants at the Hgyptian Survey Department, who spared 
no trouble to ensure the success of our expedition; Mr. 
Dowson, Mr. A. Lucas, and Mr. Dickinson were of the 
greatest assistance to us during our stay in Cairo, helping in 
the choice of servants and stores, and in the transport of our 
baggage to the Faytim. 
Mr. Dickinson, in addition, accompanied the expedition 
down to the lake, where his thorough knowledge of the 
district was invaluable and saved us much time and trouble. 
Although commenced at Cambridge the greater part of 
this work was carried out in the Zoological Laboratory of 
the Oxford University Museum, and I wish to. express here 
my sincere thanks to Professor G. C. Bourne for all the 
facilities which he afforded me. i! 
I have also to acknowledge my indebtedness to Mr. C, 
