FRESH-WATER SPONGES IN THE COLLECTION OF THE 

 UNITED STATES NATIONAL MUSEUM.— PART IV. NOTE 

 ON THE FRESH-WATER SPONGE, EPHYDATIA JAPON- 

 ICA, AND ITS ALLIES. 



By, Nelson Annandale, 

 Superintendent of the Indian Museum, Calcutta. 



Among the specimens of fresh-water sponges recently sent me by 

 the U. S. National Museum for examination is one of considerable 

 interest from the point of view of geographical distribution. Taken 

 in the Eastern Branch of the Potomac River near Washington, Dis- 

 trict of Columbia, it evidently represents Hilgendorf's Spongilla flu- 

 viatilis, var. japonica, which, as I have recently pointed out, deserves 

 to rank as a distinct species. 



Epltydatia japonica may be distinguished from the E. fluviatilis of 

 recent authors by the shortness of its birotulates, which are never 

 much longer than the diameter of their rotules, and by the fact that 

 the indentations on the edge of the rotules are much deeper. From 

 E. mulleri (Lieberkuhn) it may be distinguished by the smoothness 

 of its skeleton spicules, and from E. meyeni (Carter) by the shortness 

 of its birotulates and by the fact that they never form more than a 

 single layer on the gemmule. The following key will demonstrate 

 the most conspicuous characters of these four closely allied species, 

 which are often confused: 



I. Skeleton spicules smooth. 



A. Shafts of birotulates much longer than diameter of rotules; rotules not deeply 



indented; no vesicular cells in the parenchyma E. fluviatilis. 



B. Shafts of birotulates much longer than diameter of rotules; rotules deeply in- 



dented; vesicular cells abundant in the parenchyma E. meyeni. 



C. Shafts of birotulates not, or at most slightly, longer than diameter of rotules; 



r< itules deeply indented ; (?) vesicular cells E. japonica. 



II. Skeleton spicules conspicuously roughened (except at the tips). 



Shafts of birotulates not, or barely, longer (ban diameter of rotules; rotules 

 deeply indented; vesicular cells abundant in the parenchyma E. mulleri. 



E. fluviatilis occurs all over Europe and North America, in Siberia, 

 Japan, the Malay Archipelago, and Australia; E. mullcn all over 



Proceedings U. S. National Museum, Vol.. 38— No. 1 771 . 



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