The Sponges of Lake Biwa. 13 



at least moderately slender and sharply pointed, are densely spiny 

 in the middle region but smooth at the extremities. There are no 

 free microscleres. The gemmule-spicules are short and bear large 

 terminal rotules, which are deeply and irregularly indented round 

 the edge. The shafts are very little, if at all, longer than the 

 diamètre of a single rotule; they are usually quite smooth. The 

 rotules are flat. 



The typical form of the species, though it is known to occur 

 in Japan (Tokyo and neighbourhood), has not been found in Lake 

 Biwa, in which the following variety is found abundantly. 



var. Japoniea (Hilgendorf), nob. comb. nov. 



1909. Ephydatia japoniea, Annandale, Annot. Zool. Japon, VII, p. 119, pi. II, fig. 3. 



This variety only differs from the typical E. mullerl in having 

 skeleton-spicules that are as a rule quite smooth and bear at most 

 a few minute and scattered spines on the central region. Some- 

 times the birotulate spicules are arranged on the gemmule in 

 several tiers, and not infrequently they have one rotule distinctly 

 larger than the other. 



From JE. fluviatilis auct. the variety only differs in the pre- 

 sence of bubble-cells in the parenchyma and in the shortness of 

 gemmule-spicules, while from E. meyeni (Carter) only the latter 

 character serves to distinguish it. 



There has been much confusion between E. fluviatilis and E. 

 mulleri, and the races of E. fluviatilis called syriaca and himalayensis 

 described by Topsent and Annandale respectively seem to render the 

 recognition of the two species more difficult and more uncertain. 



E. mülleri is widely distributed in Europe and N. America 

 and is represented in Lake Baikal in northern Asia by a form that 

 seems to be more than an aberrant phase or variety. The variety 

 japoniea has been found in the Potomac River on the Atlantic 

 side of N. America. In Japan it has been reported from Tokyo 

 and Lake Aoki, Province of Shinano. In Lake Biwa it is 

 abundant, and we have also seen specimens from following 

 localities : — 



