THE SPONGES (PORIFERA) 



313 



44 (45) Rotules of gemmule spicules of small class regular mushroom-shaped, 

 shafts usually smooth. Heteromeyenia repens Potts 1 880. 



Sponge encrusting, thin. Gemmules not abundant. Skeleton 

 spicules rather slender, sparsely microspined, gradually pointed. 

 Dermal spicules nearly straight, entirely spined. Gemmule birotu- 

 lates of longer class comparatively few; shafts, smooth or with one 

 or a few conspicuous spines often irregularly bent. Rotules dome- 

 shaped, rays incurved like lish hooks. Small birotulates very nu- 

 merous, about two-thirds the length of the large ones. Quiet, 

 almost stagnant water. New Jersey, Pennsylvania, and Michigan. 



Fig. 578. Spicules of Eeteromeyenia repens. Five types of spicules 

 figured here; microspined skeleton spicules; gemmule birotulates of the 

 longer class, with recurved hooked rays; birotulates of the shorter class 

 with less pronounced rays; rotules of same; small dermal spicules, coarsely 

 spined; amorphous spicule. X lOO. (After Potts.) 



45 (44) Rotules of gemmule spicules of small class very irregular, shafts 

 abundantly spined. Heteromeyenia argyrosperma Potts 1880. 



Sponge minute, encrusting, gray. Gemmules abundant and 

 large. Foraminal tubules somewhat prolonged. Skeleton spicules 

 rather slender, cylindrical, abruptly pointed, sparsely spined. 

 Dermal spicules apparently wanting. Shafts of long birotulates 

 sparsely spined. Rays of rotules few, long, stout, and clawlike. 

 Short birotulates much smaller, abundantly spined. From Penn- 

 sylvania, New Jersey, New England States, and Nova Scotia. 

 Foimd by F. Smith at Douglas Lake, Mich. 



Fig. 579- Spicules of Eeteromeyenia argyrosperma. Three types of 

 spicules figured here; sparsely microspined skeleton spicules; gemmule 

 birotulates of the longer class with one to three booked rays; spined birot- 

 ulates of the shorter class. X loo. (After Potts.) 



46 (14) Rotules of gemmule spicules unequal, the proximal being larger. 



Tubella Carter. 

 Only North American species known. 



Tubella pennsylvanica Potts 1882. 



Sponge minute, encrusting, on stones or timbers in shallow water. 

 Gemmules very numerous, small. Skeleton spicules very variable 

 in length and curvature, entirely spined; spines large, conical. Der- 

 mal spicules wanting. Birotulates of gemmules numerous with a 

 large rotule ne.xt to the coat and a small distal rotule, varying from 

 the diameter of the shaft to that of the pro.ximal rotule. Margin of 

 large rotule usually entire but margin of small often angular and 

 notched. Shaft smooth. Averse to light and found as a rule under 

 stones and roots. Eastern United States generally. Found by F. 

 Smith at Rhinelander, Wis., and Douglas Lake, Mich. 



Fig. 580. Spicules of Tubella pennsylvanica. Two types of spicules 

 figured here; spined skeleton spicules; gemmule "inaequibirotulates." or 

 trumpet-shaped spicules; group of rotules seen from above, showing the 

 relative sizes of the rotules; surface of single large rotule. X loo. (After 

 Potts.) 



47 (13) Apertures of gemmules prolonged and divided into filamentous ap- 

 pendages. . . . . Carlerius Potts . . 48 



Gemmules possess a long foraminal 'fubule, the outer end of which carries an irregularly 

 lobed disc or is provided with long filaments. Not recognized as a separate genus by some 

 recent authors (see Annandale, 1909), but distributed among the preceding genera. 



