70 



THE SPONGES. 



structures are found, as in the other subspecies. In the shape and appear- 

 ance of these structures, however, this subspecies differs somewhat from the 

 others, in that the structures are here strongly compressed ridges, which 

 in side view appear triangular (Fig. 5, Plate 9). The longitudinal char- 

 acter of their arrangement, so conspicuous in the figure, is obviously 

 correlated with the very elongated spiral character of the sponge body. 



The dermal pinuii, Fig. 5, Plate 8, differ from those of the other sub- 

 species, tubuliferum and mucronatum, in respect to the distal ray. This 

 is noticeably thicker, with a more rounded outline, and the lower bare 

 part of the ray is very short. The ray, which may be of the same length 

 as the others, but is often shorter, is commonly about 50 xx thick, and has 

 a bare basal portion about as long as thick, measuring 16 /x x 16 /x to 

 20 /x x 20 /a. The tangential rays are in general pointed, but exceptionally 

 are rounded and enlarged at the ends, and like the other rays are some- 

 what thicker than in the two other subspecies. A characteristic spicule 

 has these measurements : distal ray, 120 /x x 50 /x ; proximal and tangential 



rays, 150 /x x 10 /x. 



Exceptional forms are found in some of which the 



development of spines on the distal ray is so great as to obliterate the 

 lower bare part ; and others of an opposite character, in which the lower 

 bare part of the ray is nearly as long as in the other subspecies. 



8, Plate 8) forms, 



The gastralia include pentact and hexact 



(Fig- 



which are alike except in respect to the distal ray. The tangential rays 

 differ noticeably from those of the type and subspecies tubuliferum and 

 mucronatum in that they are beset all over with minute sharp denticulations. 

 This denticulation may be so fine that the ray appears nearly smooth. 

 The proximal ray is also beset throughout its length with similar minute 

 prickles. The tangential rays, which are very slightly incurved, commonly 

 end, as does the proximal, in points, but exceptionally they are rounded 

 and enlarged at the ends. In a characteristic spicule the tangential rays 



measure 200 /x x 12 /x, the proximal ray 240 /x x 12 /x. 



In the pentact 



forms the distal ray is represented by a small rounded or angular boss. 

 In the hexact forms (Fig. 8, Plate 8), the distal ray, which is 100-150 /x 

 long, is in general more bushy than in the other subspecies, although it 

 varies to a nearly cylindrical spinose shaft, somewhat thickened at the top. 

 In one of the specimens the hexacts greatly predominate, in the others 

 the pentacts and hexacts are about equally abundant. In one of the latter 

 specimens the spicules vary toward the condition of the type and the 





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