Description of a freshwater sponge from the North-West 
of Siberia, 
With 4 figures. 
By N. Annandale, D. Sc., F. A. S. B., Superintendent, Indian Museum, Calcutta. 
Dr. Ph. Zaitzev lias been kind to send me for examination specimens of a sponge 
tliat he discovered in some arctic lakes in north-western Siberia, and as these specimens 
apparently represent a species that lias not hitherto been described I propose to descnbe it 
under the naine: 
Spongilla (Euspongilla) arctica, sp. nov. 
Sponge. The sponge consists of small nodular masses of a yellowish colour in spirit. 
Its oscula are few, small and inconspicuous. The surface is smooth and the consistency soft; 
tliere is a délicate brownish membrane at the base. 
Skeleton. The structure of the skeleton is peculiar and characteristic. It consists in 
the main of slender spiculé fibres each of whicli is encased in spongin. The fibres arise 
from the basal membrane, with 
which their investment is in 
direct continuity, and run 
upwards, sometimes in a slan- 
ting direction; in their course 
tliey branch frequently in a 
dichotomous manner, and dél¬ 
icate webs of spongin extend 
across the forks, often con- 
tainiug circular or oval aper- 
tures (fig. 2). Single spiculés 
or indefinite transverse fibres 
run occasionally from one 
branch to another, carrying 
with them their investment 
of spongin. In addition to the organized skeleton tliere are numerous loose megascleres 
lying free in the substance of the sponge and formiug an irregulär layer at the base. They 
Зап. Физ.-Мат. Отд. 1 
