HYALONKMA (OONEMA) SEQUOIA. 355 



guish four kinds of amphidiscs in this sponge: — 1, large macramphidiscs, 2, 

 small macramphidiscs, 3, large micramphidiscs, and 4, small micramphidiscs. 



Although the length frequency-curve of the large macramphidiscs has two 

 summits, I do not distinguish two distinct groups among these spicules, because 

 the depression between the two summits is but slight and because there are 

 no notable morphological differences between the spicules to which the two 

 parts of the curve on each side of the depression refer. 



The large macramphidiscs (Plate 86, figs. 1-6; Plate 89, figs. 31, 32; Plate 

 91, figs. 1-6) are 370-550 ti long, most frequently about 425 m- The shaft is 

 straight, cylindrical, and 19-27 ^ thick. It usually bears a few broad and low 

 quite insignificant tubercles. Some of these are often arranged in an irregular 

 verticil situated in the middle-part of the shaft, which is, at this point, usually 

 slightly thickened to an inconspicuous central tyle, only 1-3 /x, exceptionally 

 as much as 6 n, more than the adjacent parts in transverse diameter. Rarely 

 the shaft bears a larger, cylindrical, terminally rounded spine, sometimes 28 m 

 long, and 10 ^ thick (Plate 86, fig. 4). I have never observed more than one 

 such spine on the shaft of the large macramphidiscs. 



The terminal anchors are 120-170 ^ long and 200-256 ju broad. The 

 proportion of their length to their breadth is 100 : 139 to 100 : 196, on an average 

 100 : 171.3. The proportion of the anchor-length to the total length of the 

 spicule is 1 to 2.6-4.7, on an average 1 : 3.6. The anchors are usually composed 

 of eight teeth. The teeth of the two anchors of the same spicule lie opposite 

 each other in the same planes passing through the axis of the shaft. The indi- 

 vidual teeth are about 25 /n broad near the base, and pointed at the end (Plate 

 89, figs. 31, 32). Their curvature is usually greater at the base and at the end 

 than in the middle. The tip of the tooth is sometimes abruptly bent either 

 inward (Plate 91, fig. 4) or, more rarely, outward (Plate 91, fig. 1). The teeth 

 occasionally bear conspicuous, somewhat branch-like protuberances on their 

 convex outer (Plate 91, fig. 3) or concave inner side (Plate 91, fig. 2). A well- 

 marked depression can be made out, sometimes very clearly, on the apex of the 

 anchor (Plate 91, fig. 4). 



The length frequency-curve of the small macramphidiscs has two summits 

 separated by a rather conspicuous gap. The smaller ones, to which the part 

 of the curve to the left of the depression refers, have a larger number of anchor- 

 teeth than the larger ones, to which the part of the curve to the right of the 

 depression refers. Two kinds of small macramphidiscs could therefore be 

 distinguished. Since, however, the differences between them are not great and 



