The Sponges of Lake Biwa. "[7 



than with European 1 )m . that there is apparently an endemic Japan- 

 ese element among them ; and that one form is probably of 

 eastern tropical origin. 



A consideration of the genera and subgenera does not lead to 

 any definite conclusion. Spongilla and Ephydatia?' are cosmo- 

 politan, while Heteromeyenia is mainly Nearctic. Two of the three 

 subgenera into which Spongilla may be conveniently divided 

 (viz. Euspojitta and Eunap'ms) are co-extensive in range with the 

 genus, but Stratospongilla, the third subgenus, is mainly Ethiopian 

 and Oriental and to a large extent tropical. Single species occurs, 

 however, in Fiji and in South America. 



On the whole, therefore, the genera and subgenera of Spon- 

 gillidae represented in L. Biwa would merely suggest that the 

 fauna of which they form a part is of somewhat mixed origin, 

 mainly Holarctic, with perhaps Nearctic affinities, and with a cer- 

 tain endemic element, but also containing an element derived 

 from the south and possibly of Oriental origin. 



III. Bionomical. 



Lake Biwa is partially separated into two regions by a pair of 

 opposed promontories. These regions differ greatly in size and in 

 the nature of the environment they offer to animal life. The 

 smaller of the two is known locally as the South Lake, the larger 

 as the North Lake. These names may be used conveniently if it 

 be understood that there is a comparatively broad passage between 

 the two "lakes." The South Lake is nowhere more than 30 

 Japanese feet (about 9 meters) in depth; the bottom is for the 

 most part muddy, and there is a very profuse growth of water- 

 weeds. The North Lake, which is far larger than the other, has, 

 on the other hand, a depth of from 200 to 320 Japanese feet (60 

 to 97 meters) over the greater part of its area. The deepest 

 depressions have a bottom of fine mud, and sponges are apparently 



1) The sponges of the greater pari; of northern Continental Asia are still very imperfectly 

 known. 



2) Further study does not bear out the view that Ephydatiu is unusually predominant in 

 Japan (see Annandale, Annot. Zool. Japon., VIL, p. 105). 



