REVISION OF FRESHWATER SPONGES OF SPONGILLIDAE 13 



simple in all gemmules examined, or merely bears a slightly elevated 

 collar. While S. arctica displays a most unique arrangement of abun- 

 dant spongin membranes throughout its skeleton, all other criteria 

 used for its separation from S. lacustris could not serve such a pur- 

 pose. Although future revisions may demonstrate that these two 

 species should be united, it is advisable to retain the separate status 

 of S. arctica until more material will be available. 



Rezvoj (1928) listed and figured two types of microscleres, one 

 typical amphioxea, the other slender amphistrongyla. Although both 

 these scleres are also present in the type material, the latter must be 

 considered immature gemmoscleres. 



Spongilla helvetica Annandale, 1909 



Plate 1, figures 6, 7 



Spongilla (Euspongilla) helvetica Annandale, 1909a, p. 367. 



Spongilla helvetica{1) Arndt, 1926, p. 342.— Gee, 1931e, p. 39; 1932c, p. 38.— 

 Penney, 1960, p. 19. 



Material. — Fraction of type and syntype material, and sUdes 

 from these. 



Description. — Sponge, according to Annandale (1909a), forming 

 crusts of varying dimensions, without branches; surface smooth, 

 oscula distinct but small; dermal membrane dehcate and adhering 

 the symplasm. Skeleton consisting of slender spicule fibers encased 

 in spongin, and transverse spicule tracts. Consistency of live sponge 

 soft. 



Megascleres rather short and fusiform amphioxea, generally smooth, 

 very exceptionally covered with a few scattered conical spines; free 

 megascleres of smaller dimensions also both in dermal membrane and 

 symplasm; length range 148-200 p., width range 4-9 p. 



Microscleres scarcely present in dermal membrane and symplasm, 

 also sometimes in the vicinity of the gemmules; they are slender and 

 small fusiform amphioxea, covered with minute straight spines or 

 granules; length range 24-55 p, width range 1-2 p. 



Gemmoscleres rather rare, slender and shghtly curved, abruptly 

 pointed amphioxea, covered with numerous small spines which are 

 aggregated at the tips of the scleres; length range 32-68 p, width range 

 2-5 p. 



Gemmules variable in diameter, ranging 300-650 p, spherical; 

 pneumatic layer absent; gemmoscleres occasionally lying tangentially 

 on gemmular membrane, often lacking altogether; foramen or fo- 

 ramina simple, never tubular, occasionally bearing a shghtly elevated 

 peripheral collar. 



Distribution. — At present known only from the type locaHty, 

 Lake Geneva, Switzerland. 



