230 HYALONEMA (HYALONEMA) TYLOSTYLUM. 



indicate that these sponges were, in hfe, cup-shaped and that they have lost 

 their upper marginal part and have been compressed to lamellar structures 

 without open gastral cavities during or after capture. 



The colour in spirit is dull brown. 



The skeleton. The distal rays of the dermal pinnies form a dense fur on the 

 intact parts of the outer surface (Plate 70, figs. 3b, 8). Numerous amphidiscs, 

 chiefly small macramphidiscs, occur in and just below the dermal membrane. 

 The shafts of these spicules are situated radially. About one half of each of these 

 amphidiscs with one anchor protrudes freely beyond the surface; the other 

 half with the other anchor is imbedded in the sponge (Plate 70, fig. 3a). The 

 lateral rays of hypodermal pentactines extend just below the layer occupied by 

 the lateral rays of the pinnies. Large macramphidiscs with the shaft parallel or 

 oblique to the surface occur a little farther. Besides these and down the proxi- 

 mal rays of the hypodermal pentactines, small hexactine megascleres also occur 

 in this region. The skeleton of the inner gastral face of the lamellae (cup-wall) 

 consists of gastral pinnies and hypogastral pentactines. Tylostyles, hexactines, 

 numerous microhexactines, a few micropentactines, and a good many amphi- 

 discs, chiefly small macramphidiscs and micramphidiscs, are met with in the 

 choanosome amphioxes. 



The dermal pinules (Plate 70, figs. 1, 2, 3b, 8) are pentactine and have a 

 straight distal ray. One of the many observed was hexactine, and one other 

 had an angularly bent distal ray. The distal ray is 340-379 m long, most fre- 

 quently 342-368 /u, on an average 355 n, and, at the base, 8-11 m thick, generally 

 about 9 M- Its basal end-part, for a distance of about 30 n, is smooth, thence 

 onward the distal ray is spiny. The lowest spines are scarce, short, and very 

 divergent. Distally, up to a point 100-120 ^ from the tip of the ray, the spines 

 become more crowded, longer and more strongly incUned towards the ray. 

 Farther on they again decrease in length and divergence, the uppermost being 

 nearly parallel to the shaft. At the point of maximum thickness, which lies high 

 up, the distal ray, together with the spines, is 31-47 ai in transverse diameter. 

 The lateral rays are cylindrical, usually rounded at the end, spined, and 27-42 n 

 long, on an average 35 ^l. The single proximal ray observed was about as long 

 as the laterals. 



All the gastral pinules (Plate 70, figs. 9, 10) observed were pentactine. 

 Their distal ray is straight, 120-245 m long, most frequently 150-190 m, on an 

 average 166 m> find, at the base, 5-10 ti thick, generally about 8 ii. It is sharp- 

 pointed and markedly thickened some distance below the middle of its length. 



