HYALONEMA (HYALONEMA) PLACUNA. 215 



All the amphidiscs under 30.5 m and the majority of those 30.5^2 m long 

 have broad anchors (proportion of anchor-length to anchor-breadth 100 to 58- 

 92). Some of the amphidiscs 30.5-43 ^ long, and all 43-48 fi long, have more 

 slender anchors (proportion of anchor-length to anchor-breadth 100 to 50-56). 

 The few dimensionally intermediate forms 55-100 n long, and the smaller of the 

 forms belonging to the second main elevation of the curve (that is those 124- 

 286 n in length), have slender anchors (proportion of anchor-length to anchor- 

 breadth 100 to 42-66). The largest measured amphidiscs, that is those 287- 

 367 M long, have broad anchors (proportion of anchor-length to anchor-breadth 

 100 to 72-107). Among the latter two kinds can be distinguished according to 

 the shape of the anchors. In some of the smaller ones the anchors are narrow 

 at the apex and composed of teeth terminally diverging from, parallel to, or 

 only slightly converging to the shaft. In the smaller and all the larger ones, that 

 is those 328 n and more long, the anchors have a broad apex and are composed 

 of distally converging teeth. 



Taking into consideration both their length frequencies and the differences 

 in the shape of their anchors, we come to the conclusion that, as stated above, 

 seven kinds of amphidiscs are to be distinguished in this sponge: — 1, large 

 macramphidiscs with apically broad anchors; 2, small macramphidiscs with 

 apically narrow anchors; 3, large, 4, medium, and 5, small mesamphidiscs ; 6, 

 large micramphidiscs with slender anchors; and 7, small micramphidiscs with 

 broad anchors. 



The amphidiscs of form A are similar to those of form B but on the whole 

 smaller and, as stated above, not so numerous. Groups 1 and 3 contained only 

 one amphidisc each and group 5 contained none. 



The large macramphidiscs ivith apically broad anchors of form B (Plate 66, 

 figs. 3, 4) are 287-367 n, most frequently about 320 ^ long. The shaft is straight, 

 cylindrical, 8.5-11 m thick, and abruptly thickened in or near the middle to a 

 central tyle 13-17 m in diameter. An irregular verticil of truncate, cylindrical, 

 vertical or, more rarely, oblique spines 8-14 ^ long and usually about 5 m thick 

 arises from this tyle. The remaining parts of the shaft bear a smaller or a larger 

 number of exceedingly low, broad protuberances. The two anchors of the same 

 spicule are equal or unequal. Their inequality is sometimes considerable. 

 The greatest dimensional difference of the two anchors of the same spicule 

 observed was 14 ^ in the length and 13 m in the breadth. The anchors are 

 100-132 M long, usually about a third of the whole spicule. They attain their 

 maximum breadth some distance above the end, and here measure 79-118 fi in 



