The Sponges of Lake Biwa. 15 



more than 7 times, as long as the rotule. It barely projects 

 beyond it. The rotules are flat or nearly so in both cases. Their 

 margins are deeply and irregularly serrated but the individual 

 serrations are angular and rarely curved. 



The gemmules are small, somewhat flattened and as a rule 

 elliptical as seen from above. They are scattered in the interstices 

 of the skeleton. The pneumatic layer is moderately thin. The 

 foramen is protected by a stout curved tubule which expands 

 somewhat at the distal extremity but is totally devoid of process. 



Length of skeleton-spicule (average) 0. 29(5 mm. 



Transverse diameter of skeleton-spicule (average)...!). Oil mm. 



Length of shaft of shorter gemmule-spicule(average)0.042 mm. 



Length of shaft of longer gemmule-spicule (average) 0.062 mm. 



Greatest diameter of gemmule 0. 86 mm. 



Type. In the Biological Station at Otsu; a schizotype in the 



Indian Museum, Calcutta. 

 Locality. Otsu, L. Biwa (coll. T. Kawamura): Oct. 7, 1914. 



I have much pleasure in naming this interesting species after 

 T. Kawamura, my collaborator in other parts of the present paper, 

 who discovered the only known specimens. H. hawamurae is 

 closely allied, in my opinion, to Heteromeyenla (" Carterius") 

 latltenta (Potts) from North America. The most striking difference 

 lies in the structure of the foraminal tubule of the gemmule — a 

 feature which is, however, regarded by many others as of generic 

 importance. 



II. Geographical. 



The distribution of the different species of Spongillidae in 

 Lake Biwa itself will be discussed in the third section of this paper, 

 as it is essentially a bionomical rather than a geographical question. 

 Precise data are not yet available for a discussion of the distribu- 

 tion of the Spongillidae in the Japanese Archipelago. 



Of the seven species known from Lake Biwa two are as yet 

 known only from the Main Island of Japan, namely Spongilla semi- 

 spongilla (Annandale) and Heteromeyenla hawamurae Annandale. 



