REVISION OF FRESHWATER SPONGES OF SPONGILLIDAE 137 



Trochospongilla pennsylvanica (Potts, 1882) 



Plate 12, Figures 3, 4 



Tubella pennsijlvanica Potts, 1882a, p. 14; 1884b, p. 216; 1886, p. 228; 1887, 

 p. 251.— MacKay, 1885, p. 233; 1889, p. 87.— Kellicott, 1891, p. 104.— 

 Weltner, 1895, p. 114.— Girod, 1899, p. 112.— Annandale, 1908d, p. 248; 

 1909f, p. 102.— Smith, 1921, p. 17; 1930, p. 184.— Penney, 1931, p. 240; 

 1960, p. 58.— JeweU, 1939, p. 20.— Wurtz, 1950, p. 6. 



Trochospongilla pennsylvanica Annandale, 1911c, p. 118; 1912d, p. 384; 1918a, 

 p. 213.— Gee, 1926a, p. 184; 1931e, p. 46; 1931a, p. 502; 1932b, p. 22; 1937, 

 p. 285.— Arndt, 1928b, p. 164.— Old, 1932a, p. 132; 1932c, p. 239; 1932b, 

 p. 442; 1936b, p. 11.— Eshleman, 1950, p. 42.— Moore, 1951, p. 63; 1953, 

 p. 25. 



Tubella pennsylvanica var. minima Potts, 1887, p. 252. 



Trochospongilla pennsylvanica va,r. minima Gee, 1931e, p. 43; 1932b, p. 25; 1932c, 

 p. 43. 



Tubella fanshawi Potts, 1887, p. 252. 



Tubella intermedia Potts, 1887, p. 252. 



Trochospongilla pennsylvanica var. mackayi Gee, 193 le, p. 42. 



Material. — Numerous specimens and slides from the United States 

 and Canada. 



Description. — Sponge forming flat crusts of moderate dimensions; 

 surface slightly hispid and irregular, with a number of sloping emi- 

 nences surrounded by radiating furrows; oscula conspicuous but small 

 and few in number. Skeleton consisting of an irregular network, 

 joined together by very little spongin. Consistency of life sponge 

 moderately soft to fragile. 



Megascleres somewhat slender, feebly curved, sharply pointed 

 amphioxea, rarely amphistrongyla, entirely covered with small, coni- 

 cal, and sharp spines; length range 140-210 /x, width range 8-11 n. 



Microscleres absent. 



Gemmoscleres minute birotulates with slender shafts, and termi- 

 nally with rotules of more or less recurved circular margins, usually 

 of similar shape but invariably of greatly differing diameter; lower 

 rotule always normally developed, upper rotule frequently rudimen- 

 tary, sometimes irregular; length of shaft 9-11 fx, its thickness about 

 2 n; diameter of lower rotule 16-20 m, of upper 3.5-8.5 fi. 



Gemmules rather abundant, confined to lower parts of sponge, 

 spherical, and minute; apparently not encased in cages of megascleres; 

 diameter ranging 190-390 n; pneumatic layer granular and com- 

 paratively thin, rarely covering the upper rotule of gemmoscleres; 

 gemmoscleres crowded in this layer so that their lower rotules dis- 

 tinctly overlap each other; foramen produced into a conical and 

 short porus tube. 



Distribution. — Apparently restricted to the North American 

 Continent, its recorded occurrence in Ireland and Scotland needs 

 confirmation. 



