170 HYALONEMA (HYALONEMA) OBTUSUM. 



more than a third of the whole spicule, and 16-69 /x broad. The proportion of 

 the length to the breadth of the anchors is 100 to 56-96, on an average 100 : 81.2. 

 The individual anchor-teeth are strongly curved in their basal part. Distally 

 their curvature decreases and their end-parts, a third to a half of their total 

 length, are nearly straight and parallel. 



The small macramphidiscs of var. robusta are similar but stouter and pro- 

 vided with broader terminal anchors. Their measurements are: — length, 146- 

 205 fi, most frequently about 176 n; thickness of shaft 4-11 n; anchor-length 

 45-80 fi, usually a little over a third of the length of the whole spicule; proportion 

 of anchor-length to anchor-breadth, 100 to 72-112, on an average 100 : 81.2. 



The large micramphidiscs of var. gracilis (Plate 37, figs. 6-11) are 28.5-68 /x 

 long, most frequently about 32.4 fi. The shaft is O.S-1.5 m thick. It always 

 bears a few spines in or near the middle, and usually some also elsewhere. The 

 central spines do not form verticils. The spines are 0.4-1 n long, about as thick, 

 and usually cylindrical and terininally rounded, or truncate. 



The two anchors of the same spicule are very similar, the greatest difference 

 observed in thek lengths and breadths being 2 n and 1 fj. respectively. The 

 anchors are 11-24 yu in length, that is a little over a third of the whole spicule, 

 and 6-10 n broad. The proportion of the length to the breadth of the anchors 

 is 100 to 44-64, on an average 100 : 52.6. The individual anchor-teeth of the 

 smaller forms of these spicules are strongly cur\-ed in their basal parts and fairly 

 straight in their distal parts, their total curvature being such that their tips 

 are nearly parallel (Plate 37, figs. 6, 7). In the larger forms the teeth are 

 relatively longer, and the curvature of their basal part stronger, whilst their 

 end-parts are slightly curved in the opposite direction, convex to the shaft. 

 The tips of the teeth of these amphidiscs are parallel or convergent, and the 

 anchors themselves at the end sometimes as much as 3 /i narrower than in their 

 broadest, more proximal part. This gives to these spicules quite a peculiar 

 appearance (Plate 37, figs. 8-11). 



In var. robusta no amphidiscs have been observed similar to the larger forms 

 of the large micramphidiscs with distally attenuated anchors; all the large 

 micramphidiscs of var. robusta are similar in shape to the smaller forms of the 

 large micramphidiscs of var. gracilis. The dimensions of the large micramphi- 

 discs of var. robusta are: — length 27-64 ^, most frequently about 45.5 ji; 

 anchor-length 11-25 fi, about two fifths of the length of the whole spicule; 

 anchor-breadth 7-26 /z; proportion of anchor-length to anchor-breadth 100 to 

 64-104, on an average 100:84. 



