HYALONEMA (THALLONEMA) GEMINATUM. 395 



become strongly convergent, the distance between opposite teeth being 6-20 ix, 

 rarely as much as 32 fi, less than the (maximum) breadth of the anchor. 



The small maa-amphidiscs (Plate 104, figs. 9, 10, 13, 14) are 88-153 n long, 

 most frequently about 112 /z- A good many of the largest, that is of those 136- 

 153 jj. long, have anchors of only medium length and are consequently transi- 

 tional to the large macramphidiscs above described. The shaft is straight, 

 cylindrical, and 6-12 fi thick. The terminal anchors are 50-72 n long, a third 

 to half of the whole spicule, and 70-130 ^ broad. The proportion of the length 

 to the breadth of the anchors is 100 to 146-183, on an average 100 : 161.8. The 

 anchors are composed of from ten to sixteen teeth. Roughly speaking, the 

 number of teeth is in inverse proportion to the size of the spicule. The teeth 

 of the two anchors of the same spicule are often, but by no means always, situ- 

 ated alternately. The individual teeth are generally quite uniformly curved 

 through a quarter of a circle and abruptly bent inward at the end, so that their 

 tips are strongly convergent. The outer band-shaped part of the tooth attains 

 its maximum breadth in its distal portion, and is here 12-18 m broad. The end 

 is broad, rounded off, sometimes nearly truncate. 



The micramphidiscs (Plate 103, figs. 37, 38, 49-57) are 16-92 m long, the 

 larger ones, to which the conspicuous elevation near the right-hand end of the 

 curve pertains, most frequently about 76.5 m long. The shaft is straight or 

 only very slightly curved, and 0.7-5 m thick. It is simply cyUndrical or slightly 

 thickened at or near the middle to a central tyle, 0.3-0.6 ju, rarely as much as 

 1.5 M, more than the adjacent parts of the shaft in transverse diameter. Centro- 

 tyle forms are more frequent among the larger than among the smaller micram- 

 phidiscs. A larger or smaller number of small spines are scattered over the 

 whole of the shaft. In the centrotyle forms the spines arising from the central 

 tyle are usually larger than the others. The terminal anchors are 3.5-24 n 

 long, that is one fifth to two fifths of the whole spicule, and 5.5-30 m broad. The 

 proportion of the length to the breadth of the anchors is 100 to 100-200, on an 

 average 100 : 150.5. The anchors of the larger forms are on the whole relatively 

 broader than those of the smaller. The anchor is composed of a considerable 

 number of teeth; in one 24 ix broad I counted eighteen. The individual teeth 

 are, in the larger micramphidiscs, up to 5 ju broad, and pointed at the end. 



Besides the regular micrampliidiscs above described I observed a few irregu- 

 lar micramphidiscs with terminal anchors on one side much longer than on the 

 other. In these anchors the tips of the anchor-teeth lie in an oblique plane enclos- 

 ing an angle of about 45° with the axis of the shaft. The longest part of one 



