HYALONEMA (OONEMA) HENSHAWI. 331 



I do not tliiiik that any importance is to be attached to the minor irregu- 

 larities of the curve, although some of these, particularly those in the part 

 of it pertaining to the small micramphidiscs, are not inconsiderable. 



According to the above three kinds of amphidiscs are to be distinguished : — 

 macramphidiscs, larger forms with relatively large anchors; large micramphi- 

 discs, forms of medium size with rather small anchors; and small micramphi- 

 discs, small forms with rather small anchors. 



The macramphidiscs (Plate 97, figs. 7-14; Plate 98, figs. 1-7) are 114- 

 227 y. long, most frequently about 179 n. The shaft is cyhndi'ical, smooth, 

 straight, and 12-20 ^ thick. The terminal anchors are 50-111// in length, 

 about half of the whole spicule, and 70-169 m broad. The proportion of the 

 length to the breadth of the anchors is 100 to 123-187, generally 100 to 136- 

 178, on an average 100 : 156.8. The number of the teeth in an anchor is usually 

 eight. The teeth of the two anchors of the same spicule are situated alter- 

 nately, but tliis alternation is often somewhat irregular, the adjacent anchor- 

 teeth planes (of opposite teeth) not intersecting at exactly 22.5°. The outer 

 contour of the individual teeth is curved considerably in its basal part for about 

 0.4 part of the length of the tooth, cm-ved only slightly beyond that up to 

 about 0.8 of this length, and curved again strongly at the end, so that the tips 

 of the teeth become strongly convergent. The outer band-shaped part of the 

 tooth attains its maximum width somewhere beyond the middle of its length, 

 and here measures 20-31 yu in transverse diameter. The tip of the tooth is 

 rounded or, more rarely, somewhat pointed, like a gothic arch. The keel, 

 in the larger forms, is o\'er 30 /u high at the base, and becomes gradually lower 

 distalh'. It terminates before reacliing the end of the tooth. 



Somewhat irregular forms are not infrequent among these amphidiscs. 

 Considerable inequaUties in the two anchors of the same spicule (Plate 98, 

 fig. 6) or in the teeth of the same anchor (Plate 98, fig. 4) are often met, and some- 

 times irregularities occur on the apices of the anchors (Plate 98, fig. 7). 



The large micraj?iphidiscs (Plate 97, figs. 16-20) are 67-91 n long, most 

 frequently about 69.5 m- The shaft is straight, centrotyle, and 2-4 n thick. 

 The tyle passes gradually into the adjacent parts of the shaft. It is 3.5-5 n 

 in transverse diameter, that is 0.5-3 n more than the adjacent parts of the 

 shaft. With the exception of its end-parts, the whole shaft is covered with 

 spines. The spines on the tyle are much larger than the others, sometimes 3 n 

 long, and often strongly curved. The terminal anchors are 20-35 m, usually 

 a little more than a tliird of the whole spicule in length. Their breadth is 18- 



