HYALONEMA (PRIONEMA) CRASSUM. 283 



both towards the base and towards the tip. The end of the tooth is simply 

 rounded. From the lateral margins of the teeth pointed triangular protuberances 

 arise, which stand close together and render these margins serrated. The saw- 

 teeth are, in the middle-part of the tooth, about 1 n high, 2 fx broad, and vertical. 

 Distally they become narrower and smaller and more and more directed back- 

 wards (Plate 107, figs. 17-20). The rounded distal ends of the teeth are smooth. 



The large inicraviphidiscs are 42-61 y. long, most frequently about 52 n. 

 Their length frequencj^-curve is rather broad and irregular in so far as it exhibits, 

 besides the main summit at about 52 /x, another insignificant one at about 63 ii. 

 The shaft of these amphidiscs is straight, spiny, sometimes centrotyle, and 1.5- 

 2.3 M thick. 



The terminal anchors are 17-22 ^ long. The whole spicule is 2.2-3 times 

 as long as its anchors. The maximum anchor-breadth is 9-14 /z. The end- 

 breadth is equal to the maximum breadth or slightly smaller, sometimes as much 

 as 4 11. The proportion of anchor-length to anchor-breadth is 100 to 53-72, 

 on an average 100 : 62. 



The individual teeth, which arise vertically from the shaft, are strongly 

 bent in their basal part and only slightly bent or nearly straight in their distal 

 part, so that their tips are nearly parallel or slightly convergent. 



The small micramphidiscs (Plate 106, figs. 13-25) are 13.5-36 n long. Their 

 length frequency-curve is rather broad and irregular. It exhibits two equally 

 high main sunamits at about 18.4 and 22.1 /n, and one insignificant summit at 

 about 27 fi. The shaft of these amphidiscs is straight, cylindrical, 0.8-1.2 ix 

 thick, rough or smooth, and usually centrotyle. The tyle, which exceeds the 

 adjacent parts of the shaft 0.2-1 m in transverse diameter, is often a good distance 

 away from the middle of the length of the spicule. 



The terminal anchors are 3.5-14 yu in length, a fifth to a third of the whole 

 spicule, and 5-9 m broad. The proportion of anchor-length to anchor-breadth 

 is 100 to 61-162, on an average 100 : 119.4. The largest of these smaU micram- 

 phidiscs, that is those over 30 m in length, are transitional to the large ones above 

 described, not only in respect to size, but also in respect to anchor-shape. The 

 proportion of anchor-length to anchor-breadth is in these spicules on an average 

 100 : 65. In all the small micramphidiscs, that is in those under 30 m in length, 

 the anchors are broader than long, the average proportion of anchor-length to 

 anchor-breadth being in these spicules 100 : 125.6. 



The anchor-teeth of these spicules are generally strongly and rather abruptly 

 bent at a point a third of their length from the base, and only shghtly curved 



