3io 



FRESH-WATER BIOLOGY 



29 (28) Shafts of birotulates slightly if any longer than diameter of rotules. 



Ephydatia japonica (Hilgendorf) 1882. 



Much like E. fluviatilis. Dermal spicules wanting. Birotulates with smooth shaft, short, 

 never forming more than a single layer on the gemmule. Rotules deeply indented. Gem- 

 mule with short, straight, broad, very delicate foraminal tubule. In Potomac River, near 

 Washington, D. C. 



FIG. 569. 



Ephydatia japonica. Gemmule, X 18; birotulates, X 120; skeleton'spicules, X 120. 

 (After Annandale.) 



30 (27) Skeleton spicules microspined except at tips. 



Ephydatia miilleri (Lieberkuhn) 1856. 



Sponge cushionlike, rarely branched. Vesicular cells abundant 

 in the parenchyma. Dermal spicules wanting. Shafts of gemmule 

 birotulates not, or barely, longer than diameter of rotules. Rotules 

 deeply indented. Eastern and Central United States; Nova Scotia; 

 Newfoundland; Vancouver Island. Found by F. Smith at Douglas 

 Lake, Mich., and Tolland, Col. 



FIG. 570. Spicules of Ephydatia mutter i. Three types of spicules figured 

 here: skeleton spicules, X 120; birotulate gemmule spicules; same mal- 

 formed; group of rotulae; single rotules showing an ordinary distribution of 

 the rays. X 250. (After Potts.) 



31 (26) Shafts of birotulates with enormous spines. 



Ephydatia robusta (Potts) 1887. 



Sponge massive, encrusting, thin. Gemmules scarce. Skeleton 

 spicules pointed, smooth. Birotulates large, generally malformed. 

 Shafts abounding in spines as long as rays of the rotules. Collected 

 near Susanville, California. Perhaps only a variety of E. fluviatilis. 



FIG. 571. Spicules of Ephydatia robusta. Three types of spicules figured 

 here: smooth skeleton spicules; coarsely spined gemmule birotulates; single 

 rotules; exceedingly misshapen forms. X 100. (After Potts.) 



32 (25) Length of birotulates more than twice the diameter of the rotules. . 33 



33 (34) Birotulates two or three times longer than the diameter of the rot- 

 ules Ephydatia subtilis Weltner 1895. 



Sponge thin, encrusting. Skeleton needles extremely slender, scantily covered with short 

 spines. Dermal spicules wanting. Gemmules small, spherical; foramen a simple pore, or a 

 very short tube. Birotulates delicate, slender, of variable length; shaft thin, smooth, long. 

 Rotules small, split nearly to the center, with 10 to 20 blunt rays. Kissimee Lake, Florida. 



No figure yet published. 



