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THE SPONGES. 



71 



other subspecies, in that the tubercles on the tangential rays are strong 

 prickles and are more abundant on the distal surface of the ray. 



The uncinates do not differ from those of the other subspecies. 



The hexasters are onychasters, Fig. 4, Plate 8. The claws at the 

 ends of the terminal rays are more distinctly developed than in subspecies 

 tubuliferum, the diameter of the whole disc being about 4 p. The principal 

 ray is commonly 8 /x long, the terminals 28-32 /x long. Smaller sizes, with 

 principal ray 6 /x and terminals 20 p long, are present. 



The characteristic dermal scopulae are small forms (Fig. 9, Plate 8). 

 The distal rays, 4 in number, are roughened with minute denticulations, 

 are practically straight and taper conspicuously from the base to the apex, 

 which is smooth, rounded, and not enlarged. The divergence of the rays 

 varies, being sometimes so slight that the rays look nearly parallel. In 

 different spicules the size of the terminal ray varies from a length of 50 /x 

 with a lower diameter of 4-5 /x and an upper diameter of 2 /x, to a length 

 of 70 /x with a lower diameter of 6 p and an upper diameter of 3 /x. The 

 shaft, about 300 /x long by 6-8 /x wide above, is smooth or nearly so, 

 straight or slightly curved, and tapers evenly to the point. Above it 



The spicule varies. The tapering of 



passes gradually into the rays. 



the rays may be slight, and a small head may be developed, in which 

 case it is only the slight difference in the shape of the upper end of the 

 shaft which distinguishes the spicule from the dermal scopula of subspecies 



tubuliferum. 



Mingled with the dermal scopulae just described, and quite as common, 



are scopulae 600-700 xt long, with 4-6 nearly cylindrical roughened rays 

 70-100 p long by 3-5 p thick. The rays terminate in small and feebly 

 spinose heads, 6 /x in diameter, or in large and strongly spinose heads up 

 to 12 /x in diameter. This type of scopula is similar to the smaller forms 

 found on the gastral surface. The characteristic dermal scopula (Fig. 9, 

 Plate 8), also resembles in shape one of the gastral forms (Fig. 1, Plate 9), 

 although it is very much smaller. 



The gastral scopulae, Figs. 1, 3, Plate 9, are large forms 600-1500 /x 

 lono-, the commonest sizes ranging between 600 and 800 /x. The larger 

 forms frequently penetrate the entire tube wall, even where the latter 

 consists of 5 or 6 layers of beams. The shaft is 8-16 /x thick, pointed, 

 smooth, or with a few denticulations. Above it has not a definitely cir- 

 cumscribed enlargement, but passes gradually into the rays. The rays, 



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