170 
HYALQNEMA (HYALONEMA) OBTUSUM. 
more than a third of the whole spicule, and 16-69 m 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 /d, most frequently about 176 m! thickness of shaft 4-11 n; anchor-length 
45-80 /d, 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 m 
long, most frequently about 32.4 The shaft is 0.8-1. 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 /x long, about as thick, 
and usually cylindrical and terminally rounded, or truncate. 
The two anchors of the same spicule are very similar, the greatest difference 
observed in their lengths and breadths being 2 n and 1 ^ respectively. The 
anchors are 11-24 ^ in length, that is a little over a third of the whole spicule, 
and 6-10 ,u 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 curved 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 m 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 /d, most frequently about 45.5 /x; 
anchor-length 11-25 m, about two fifths of the length of the whole spicule; 
anchor-breadth 7-26 /x; proportion of anchor-length to anchor-breadth 100 to 
64-104, on an average 100:84. 
