Bie CHARLES LL. BOULENGER, 
for in them we find the generative cells regularly distributed 
over the whole of the base of the digestive sac. 
It is a more difficult matter to find a position for the 
hydroid stage among the numerous families of the Gymno- 
blastea, certain of the characters, for instance the hollow 
tentacles and the methods of asexual reproduction, being 
quite unique among colonial Hydrozoa. | 
On the whole the family to which it bears the greatest 
resemblance is that of the Bougainvilliide, the points of 
similarity being the single circlet of filiform tentacles and 
the cylindrical hypostome not constricted off from the body 
of the hydranth. 
The new genus may be defined as follows :— 
‘‘Hydrocaulus consisting of long unbranched stems rising 
at short intervals from a small horizontal hydrorhiza, the 
latter invested by a delicate annulated perisare continued 
onto the bases of the stems. 
“Hydranths claviform with a small number (commonly 
four or five) of hollow filiform tentacles arranged in a circlet 
around the thickest part of the body. 
“ Hypostome cylindrical, not constricted at its base. 
Asexual reproduction by budding and transverse fission. 
“Medusa developed from the body of the hydranth; when 
liberated globular with four unbranched radial canals and 
tentacles. Mouth simple. Manubrium very short; the 
stomach region provided with per-radial pouches which in 
the adult are produced into finger-shaped diverticla extending 
down the sub-umbrella. Gonads developed‘on the whole 
surface of the stomach and its diverticula.” 
IV. ConcLuUsIoNs REGARDING ORIGIN, 
The occurrence of a new medusa in the waters of the Nile 
system is of great interest. It is true that the water of Lake 
Qurun is decidedly brackish, and that therefore the term 
freshwater medusa cannot with strict accuracy be applied to 
