32 Dr. W. DybowskI ow Lubomlrskia balcalensis. 



mirror, if we go about in a boat we can delight ourselves 

 with the sight of numerous beautiful colonies of sponge- 

 bushes growing up from the bottom of the lake. The bushy- 

 sponges sometimes attain an enormous size. One of them 

 brought up by the dredge was so large that it by itself filled 

 the whole bag of the dredge ■^. Such large stocks, however, 

 are rare ; usually the size of the sponge-bushes does not 

 exceed 60 centim. 



At a depth of 6-25 metres, arborescent or fruticose sponges 

 occur ; at greater depths only cushion- or turf-like sponges. 



At a depth of 100 metres (the greatest depth at which 

 sponges have as yet been taken) we find only occasionally a 

 few small and flat stocks, and even these only when the above- 

 mentioned conditions are realized. 



On the eastern shore the bottom of the lake is generally 

 covered with sand or with small easily movable stones ; there- 

 fore the s]3onges are here much scarcer. On the larger blocks 

 the sponges oidy rarely occur, because the west winds, which 

 are here prevalent, cau.se a continual succession of waves, 

 which is evidently injurious to the growth of the sponges. 

 On the rocky terraces of the shore there are a few cushion-like 

 sponges, but not in such abundance as on the other side, on 

 the western coast of the lake. 



In the Angara (see Dybowski, /. c. fig. 1) the sponges occur 

 everywhere in great abundance from the mouth up to the 

 Taltzinskaja manufactory. They are exclusively turf-like or 

 lamelliform sponges, which adhere to large logs of wood and 

 blocks of stone or to smaller pieces of wood ; arborescent 

 forms never occur ; evidently the sponges require still water 

 in order to become developed in the arborescent form. 



Between the Taltzinskaja manufactory and the city of 

 Irkutsk sponges occur much more rarely, as here large stones 

 and logs of wood are less numerous. Above Irkutsk the 

 Angara has not yet been examined for sponges. 



If we briefly summarize all that is known with regard to 

 the distribution of the Baikal sponges, the following may be 

 said : — 



1. Close to the shore of the lake, at a depth of 2-6 metres, 

 only turf- like. 



2. Ax a depth of 6-25 metres, arborescent or fruticose. 



3. At a depth of 25-100 metres turf-like stocks again occur. 

 At all these depths, of course, the sponges only exist under 

 the above mentioned favourable conditions. 



* The Ijag holds about 40 pounds of mud. 



