HYALONEMA (PRIONEMA) AZUERONE. 271 



teeth. The individual teeth arise nearlj^ vertically, are strongly and usually 

 somewhat abruptly bent a short distance from their point of origin, and only 

 slightly curved, conca\'e to the shaft in their distal and middle-parts. The 

 curvature is usually such that the end-parts of the teeth diverge from the shaft at 

 angles of about 6°. Rarely the teeth are more strongly curved, so that their 

 end-parts become nearly parallel to the shaft and to each other. The end-parts 

 of such teeth are either straight or slightl.y curved outwards. 



The small mesamphidiscs are rare. They connect the medium-sized mesam- 

 phidiscs described above with the slender-shafted micramphidiscs described 

 below. The small mesamphidiscs are usually about 44 /x long, have shafts 

 about 1.5 ,u thick, and anchors measuring 15-18 /z in length and 11-16 /j. in breadth. 

 The average proportion of anchor-length to anchor-breadth is 100: 81. 



The large stout-shafted micramphidiscs (Plate 57, fig. 9) are 38-68 yu long, 

 most frequently about 43 /.i. The shaft is straight, 1.8-2.5 ^ thick, for the greater 

 part of its length, and abruptly thickened in or near the middle to a more or less 

 irregular central tyle, usually 4-6 /x in diameter, sometimes as much as 8 yu. The 

 proportion of the thickness of the shaft to that of the tyle is 100 to 160-320, on 

 an average 100:239.8. The whole of the shaft, including the central tyle, is 

 more or less spiny. The spines of the tyle are generally larger than the others 

 and arranged in a ^'erticillate manner. The anchors are usually irregular, the 

 teeth on one side often being considerably longer than those on the other. The 

 two anchors of the same spicule usually have the longest teeth on opposite sides, 

 exceptionally on the same side. The maximum length of the anchor, that is the 

 anchor-length on the side where the teeth are longest, is 15-42 /x, sometimes more 

 than half the length of the whole spicule. On the opposite side the anchor is 

 usually 4-10 n shorter. The breadth of the anchors is 8.4-21 ju. The propor- 

 tion of the maximum length to the breadth is 100 to 45-91, on an average 100: 

 66.4. The individual teeth arise vertically from the end of the shaft and are 

 strongly curved in their basal part. Farther on the curvature decreases and their 

 end-parts are curved only slightly, concave to the shaft, or are straight, or even 

 curved slightly in the opposite direction. In no case do the end-parts of the teeth 

 diverge much from a direction parallel to the shaft, either one way or the other. 

 When, as sometimes happens, the longest teeth of the two opposite anchors lie 

 on the same side of the spicule and are, both together, longer than the whole 

 spicule, their end-parts lie side by side, but do not coalesce. 



The small stout-shafted micramphidiscs (Plate 57, figs. 10-12) are 23-34 ^l 

 long, most frequently about 32 ii. They are similar to the large ones, but have 



