THE SPONGES (PORIFERA) 309 



19 (16) Margins of rotules serrated or incised. . Ephydatia Lamouroux. . 20 



Spongillidae with gemraule spicules of the birotulate type that are uniform or variable in 

 length but not definitely of two classes, long and short, and that have finely or deeply cut 

 margins. 



20 (35, 36) Dermal spicules if present neither birotulate nor stellate. . . 21 



21 (22) Rays and spines of birotulates subdivided and microspined. 



Ephydatia subdivisa (Potts) 1887. 



Sponge massive, encrusting, compact. Gemmules few. Skeleton 

 spicules smooth or microspined, abruptly pointed. Birotulates very 

 numerous, robust, shafts frequently spined; rays short but subdi- 

 vided. From St. Johns River near Palatka, Florida. 



FIG. 567. Spicules of Ephydatia subdivisa. Three types of spicules figured 

 here: smooth and spined skeleton spicules; long, massive gemmule birotu- 

 lates, spined and subspined; rotules of same. X 100. (After Potts.) 



22 (21) Rays and spines of birotulates entire 23 



23 (24) Margins of rotules very finely serrate. 



/ 



Ephydatia millsii (Potts) 1887. 



Sponge encrusting. Gemmules small. Skeleton spicules nearly 

 straight, slender, rather abruptly pointed, entirely microspined. 

 Gemmule birotulates very numerous, very symmetrical, their shafts 

 usually smooth. Rotules sometimes microspined. From Sherwood 

 Lake, near Deland, Florida. 



FIG. 568. Spicules of Ephydatia millsii. Three types of spicules figured 

 here: microspined skeleton spicule; mature gemmule birotulates with smooth 

 ("} shafts; probably immature forms with less notching on the rotules; face 



of rotulates lacinulate or delicately notched, and without rays. 

 (After Potts.) 



X 100. 



24 (23) Margins of rotules coarsely dentate 25 



25(32) Length of birotulates not more than twice the diameter of rotules. . 26 



26 (31) Shafts of birotulates generally smooth 27 



2 7 (3) Skeleton spicules smooth 28 



28 (29) Shafts of birotulates much longer than diameter of rotules. 



Ephydatia fluviatilis (auctorum) . 



Sponge sessile, massive, rarely throwing out short branches an inch or less in length. Pre- 

 fers standing water. No vesicular cells in parenchyma. Gemmules numerous throughout. 

 Skeleton spicules smooth. Dermal spicules wanting. Rotules of gemmule spicules not deeply 

 indented. Numerous varieties the occurrence of which in North America has not been accu- 

 rately recorded. The form which Potts describes as present generally throughout the eastern 

 and middle United States is declared by Weltner to be Ephydatia miilkri, the second following 

 species. The true E. fluviatilis is found in Michigan and Illinois, and is fairly common though 

 not so abundant as E, mulleri (fide F. Smith). 



