HYALONEMA (HYALONEMA) GRANDANCORA. 241 



rically by a distinct gap in the length frequency-curve. The large macramphi- 

 discs form, as the graph shows, a biometrically perfectly homogeneous group. 



Also among the micramphidiscs two morphologically and biometrically 

 distinct kinds can be distinguished: — a larger kind, over 37 m in length, with 

 longer anchors and stout central tyle; and a smaller kind, under 31 ai in length, 

 with shorter anchors and a relatively much smaller central tyle, or no central 

 tyle at all. The part of the length frequency-curve pertaining to the first, 

 larger kind of iTiicrampliidiscs shows several ups and downs, so that this group 

 cannot be considered biometrically homogeneous. However, in view of the 

 morphological similarity of these larger micramphidiscs of various size, I do not 

 tliink the depressions in this part of the curve (none of which extends down to 

 the base (0) line) sufficient for a division of them into secondary groups. The 

 second, smaller kind of micramphidiscs forms a biometrically homogeneous 

 group. 



I distinguish accordingly four kinds of amphidiscs in this sponge: — large 

 macramphidiscs, small macramphidiscs, large micramphidiscs, and small micr- 

 amphidiscs. 



The large macramphidiscs (Plate 78, figs. 16-19; Plate 79, figs. 1, 2, 26) 

 are 318-510 ^ long, most frequently about 415 m- The shaft is generally straight, 

 very rarely bent, cylindrical, 20-26 m thick, and thickened gradually towards 

 the ends, and abruptly in or near the middle to a central tyle 24-30 ^ in trans- 

 verse diameter, that is 3-7 m more than the adjacent parts of the shaft. The 

 central tyle bears a verticil of truncate conical spines. These spines are usually 

 fairly equal, 10-20 m long and 10-12 n thick at the base. Sometimes one or two 

 are large and the others more or less rudimentary. The remaining parts of the 

 shaft are either quite smooth (Plate 79, fig. 2), or they bear only one or very 

 few protuberances, about as broad as the spines of the central tyle, but 

 generally much shorter. 



The terminal anchors are 83-125 ^ long, a quarter to a sixth of the whole 

 spicule, and 135-200 m broad. The proportion of anchor-length to anchor- 

 breadth is 100 to 142-190, on an average 100 : 165.4. The anchor consists of 

 eight teeth. The individual teeth arise vertically from the end of the shaft, 

 and are curved more strongly in their proximal than in their distal half. The 

 extreme tips of the teeth are sometimes slightly and abruptly bent inwards. 

 The curvature of the teeth is, on the whole, such that their end-parts generally 

 diverge slightly from the axis of the shaft. 



The dimensions of the single synall macramphidisc observed are : — length 



