HYALONEMA (SKIANEMA) UMBRACULUM. 
389 
then the end is attenuated and bluntly pointed (Plate 102, fig. 5). The distal 
end-parts of the outer band-shaped portions of the teeth are abruptly bent 
inward and strongly convergent, so that the distances between the ends of 
opposite teeth are 5-15 n less than the (maximum) breadth of the anchor. The 
keel retains a considerable height to within a short distance of the end of the 
tooth, and then terminates more or less abruptly. Seen in profile the tip of 
the tooth therefore resembles an eagle’s beak. 
The large micramphidiscs (Plate 103 , figs. 31-36) are 54-99 n long, most 
frequently about 84.2 /x. The shaft is 2.6-4. 5 m thick, straight, or, rarely, 
curved. Sometimes it is slightly thickened at or near the middle, sometimes 
no trace of a central tyle can be detected. The tyle is, when present, sometimes 
1.4 /x more than the adjacent parts of the shaft in transverse diameter. The 
surface of the shaft is somewhat undulating and spiny. The spines are usually 
very minute; sometimes a few larger ones arise from the central tyle. The 
terminal anchors are 10-23 /x long, one fifth to one fourth of the whole spicule, 
and 14-36 m broad. The proportion of the length to the breadth of the anchors 
is 100 to 107-200, on an average 100 : 150.9. The anchor-teeth arise vertically 
from the ends of the shaft, are either strongly bent a short distance from their 
base and slightly curved in their distal and middle-parts, or curved with a 
radius increasing distally in a uniform manner. Their tips diverge. The teeth 
are sharp-pointed at the end, and attain a maximum breadth of about 4 n- 
The small micramphidiscs (Plate 103 , figs. 27-29) are 16-38.7 n long, most 
frequently about 19.2, 26.8, and 34.2 /x. 1 The shaft is straight or, rarely, some- 
what curved, 1.2-1. 9 n thick, spiny, and sometimes slightly thickened in or 
near the centre to a small tyle. The spines are generally very minute ; exception- 
ally one or two of the central ones attain a length of 1 p. The terminal anchors 
are similar to those of the large micramphidiscs, but narrower. They are 4.5- 
10 m long, usually a little less than a third of the whole spicule, and 5.3-14 ^ 
broad. The proportion of the length to the breadth of the anchors is 100 to 96- 
157, on an average 100 : 128.1. 
The nearest allies of the above sponge are Hyalonema ( Skianema ) aequatoriale 
and H. ( Thallonema ) geminatum described in this Report. From H. ( S .) aequa- 
toriale it differs chiefly by the absence of spheres and the smaller average size 
of the microhexactines and large micramphidiscs; from H. ( T .) geminatum by 
the absence of geminate macramphidiscs and differences in the shape of the small 
macramphidiscs, the micramphidiscs, and the pinules. 
1 1 give these three numbers because the length frequency-curve pertaining to these spicules has three 
nearly equally important elevations. 
