ON MM@RISIA LYONST. 357 
On Mecrisia lyonsi, a New Hydromedusan 
from Lake Qurun. 
By 
Charles LL. Boulenger, B.A., 
King’s College, Cambridge. 
With Plates 22 and 23. 
INTRODUCTION. 
Durine the months of March, April, and May of last year 
Dr. Cunnington and I were engaged in making a biological 
survey of the Birket el Qurun, a large lake in the Faytim 
province of Heypt. 
It is situated on the edge of the Libyan desert only a few 
miles from the spot where the wonderful fossil mammals 
have recently been discovered. 
Of late years much attention has been devoted to the 
geology and topography of this interesting district, but 
nothing was known of the invertebrate fauna of the lake ; 
it was to furnish the desired biological information that we 
were invited by the Egyptian Survey Department to make 
an investigation in the spring of this year. 
The Birket el Qurun has a very unique interest as the 
remains of the historic Lake Mceris which was used as an 
artificial regulator of the Nile floods by the monarchs of the 
twelfth Dynasty. 
At the present day the lake, which is about the size and 
shape of the Lake of Geneva, communicates with the Nile 
by means of a network of canals which irrigate the Faytim, 
VOL. 52, PART 3.—NEW SERIES. 28 
