THE SPONGES (PORIFERA) 



307 



7 (8) Tubules of gemmules turned upward or outward from the groups. 



Spongilla fragilis Leidy 1851. 



Sponge encrusting in subcircular patches, thin at edges, occasionally one or more inches 

 thick near the middle. In the most varied situations, apparently preferring standing water, 

 though also in running water. Abundant. Gemmules abundant, primarily in one or more 

 pavement layers. Also in compact groups surrounded by a cellular parenchyma charged with 

 subcylindrical spined acerates. Skeleton spicules smooth, sUghtly curved, rather abruptly 

 pointed. True dermals wanting. Found in most of the United States. 



Fig. 562. Spongilla fragilis. A. Section of group of gemmules; a, curved foraminal tubules, always out- 

 ward; ft, envelop with acerate sjjicules. X 12. 5. Three types of spicules figured here; skeleton spicules, 

 smooth, abruptly pointed; variable parenchymal spicules, subcylindrical, subspined; spined, spherical 

 forms frequently seen throughout the species. X loo. (After Potts.) 



8 (7) Tubules of gemmules turned inwards in tlie groups. 



Spongilla igloviformis Potts 1887. 

 Sponge brown, thin, encrusting. Gemmules in compact hemispherical groups of eight to 

 twelve or more, resting on the fiat side, surrounded by a parenchyma of unequal cells, charged 

 with numerous coarsely spined spicules nearly as long as the rather few, less strongly spined 

 skeleton spicules. On the lower side of timbers in cedar swamps, New Jersey. S. mackayi, 

 described by Carter from Newfoundland, may belong here. 



Fig. 563. Spongilla igloviformis. A. Lateral view of dome-shaped group of gemmules. (Foraminal 

 tubules open inward and are invisible.) X 25. B. Two types of spicules figured here; skeleton spicules, 

 weakly spined: " parenchymal spicules " nearly equally long, but more spinous. X 100. (After Potts.) 



9 (6) Gemmules not in layers or groups lo 



10 (11) Dermal spicules birotulate. . . . Spongilla novae-terrae Potts 1886. 



Sponge encrusting, gemmules rather numerous, very large, crust 

 absent or inconspicuous. Skeleton spicules relatively few, slender, 

 gradually pointed, smooth or microspined. Dermal spicules very 

 abundant, minute, birotulate. Gemmule spicules smooth or irregu- 

 lar, furnished with long spines, frequently located near the extremi- 

 ties. Placed by some in genus Ephydalia. Found only in shallow 

 water of lakes in Newfoundland (48° N. L.). 



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Fig. 564. Spicules of Spongilla novae-terrae. Representing the slender, 

 smooth or sparsely microspined skeleton spicules; the dermal spicules, birot- 

 ulates of unequal size; and the spinous gemmule spicules. X lOo. 

 (After Potts.) 



