12 U.S. NATIONAL MUSEUM BULLETIN 272 



correspond in all details with the descriptions of Spongilla lacustris 

 Auct. in previous literature. 



Spongilla arctica Annandale, 1915 



Spongilla (Euspongilla) arctica Annandale, 1915d, p. 1; 1918a, p. 211. — Rezvoj, 

 1928, p. 220; 1929a, p. 284.— Arndt, 1931, p. 35.— Penney, 1960, p. 13. 



Material. — Fraction of type, and two slides obtained from the 

 type specimen by N. Gist Gee. 



Description. — Sponge, according to Annandale (1915d), consist- 

 ing of small nodular masses; surface smooth, oscula few and incon- 

 spicuous; a delicate brownish membrane present at the base, dermal 

 membrane well developed. Skeleton consisting of slender spicule 

 fibers each encased in spongin, and arising from the basal membrane, 

 running upwards at a slanting angle ; these fibers frequently branch- 

 ing in a dichotomous manner with delicate webs of spongin extending 

 across the forks; single spicules or definite transverse fibers occasion- 

 ally running from one branch to another; in addition to the organized 

 skeleton numerous loose megascleres free in the symplasm of the 

 sponge, and forming an irregular layer at the base; or forming cages 

 around single gemmules or groups of gemmules. Consistency of live 

 sponge soft. 



Megascleres of greatly varying size, in the majority small, slender, 

 fusiform amphioxea, entirely smooth; length range 154-280 (x, width 

 range 4-14 /z. 



Microscleres present in dermal membrane but apparently absent 

 from symplasm, very small, slender, and fusiform amphioxea, covered 

 with minute straight spines; length range 32-70 n, width range 2-4 ju. 



Gemmoscleres rather robust and slightly curved amphistrongyla, 

 covered with comparatively few but stout spines that are more 

 numerous at the tips of the scleres; length range 80-140 n, width 

 range 4-6 ijl. 



Gemmules variable in diameter, ranging 300-700 n, spherical; 

 pneumatic layer usually extremely thin, often totally absent; gemmo- 

 scleres scarce, embedded in this layer tangentially ; foramen typical 

 for the genus, simple, or bearing a slightly elevated small collar, not 

 tubular. 



Distribution. — Ranging from the Arctic Circle to central U.S.S.R. 



Color in life. — Not yet observed. 



Discussion. — Annandale's (1915d) original description is in part 

 erroneous, and Rezvoj (1928) as well as Arndt (1931) have corrected 

 some apparent misconceptions. An examination of the type material 

 revealed that the pneumatic layer of the gemmules is invariably 

 ill-defined to completely lacking, quite contrary to Annandale's 

 statement; also the porus, described by Annandale as tubular, is 



