I9I4'] N. Annandale : Sponges of Lake Baikal. 147 



media. Of the former Dybowski and others have described 

 varieties ; these I have experienced great difficulty, owing to the 

 existence of intermediate forms, in distinguishing. Soukats- 

 choff's Lubomirskia tscherskii and L. fusifera are possibly no more 

 than varieties of L. bacilli f era. but L. papyracea^ Dybowski and 

 L. irregularis, vSwart,, appear to be specifically distinct. 



Family SPONGILLIDAE 

 Subfamily SPONGILLINAE. 



Swartschevski (1901 ; pis. iv (figs. 13-15) and v), in a paper writ- 

 ten throughout in Russian, has described a Spongilla and two forms 

 of Ephydatia from Lake Baikal ; it should be possible to recognize 

 all of them from his figures, if not from Korotneff' s German des- 

 criptions (iQOi ; p. 307). He has named them Spongilla microgeni' 

 mala, Ephydatia olchonensis and E. goriaevii. 



All these sponges are remarkable for the abnormal character 

 of their microscleres and I am inclined to think that they represent 

 merely abortive varieties or phases^ respectively of Spongilla 

 lacustris, auct., Ephydatia mulleri, Liebk. and E. flitviatilis, auct. 

 Without examining specimens it is, however, impossible to insist 

 on this opinion. 



2 . — Geographical. 



In view of the foregoing observations it seems to be possible 

 to consider the sponges of Lake Baikal from a geographical point 

 of view under three headings, (i) sponges of marine origin, (2) 

 sponges of uncertain origin, and (3) undoubted freshwater forms. 



(i) In the first of these categories belong the two species assigned 

 here to the genus Lubomirskia. The better-known of these [L. bai- 

 calensis) has actuall}'' been found in Behring's Straits, while the 

 other is very closelj^ allied to it. All other Chalininae are marine, 

 but several species occur in semi-detached bodies of water such as 

 the Black Sea. 



(2) Although the affinities of Baikalospongia are doubtful, it 

 seems probable that its species are derived from a marine stock. 



(3) The true Spongillidae that occur in Lake Baikal are all 

 abnormal forms. 



The evidence therefore, such as it is, points to a marine 

 origin for the greater part of the sponge-fauna of the lake. There 

 is nothing definite to connect it with any other sponge-fauna but 

 that of the Arctic Sea, but possibly a remote relationship other 

 than convergent may exist between Lubomirskia and the species 

 described from Lake Tanganyika by Evans as Spongilla moorei. 

 Personally I am of the opinion that the resemblance is merely 

 another instance of convergence, a phenomenon of constant re- 

 occurrence in the Monaxon sponges, But here again, in the absence 

 of embryological evidence, dogmatism is impossible. 



The species Lubomirskia baicalensis, existing as it does both 

 in the Arctic Sea and in Lake Baikal, and, moreover, being 



