282 HYALONEMA (PRIONEMA) CRASSUM. 
I designate the four groups of amphidiscs: — smooth macramphidises (group 
1); serrated macramphidises (group 2); large micramphidises (group 3); and 
small micramphidises (group 4). 
The smooth macramphidiscs (Plate 108, figs. 14-17) are 290-370 » long, most 
frequently about 337 4. Their length frequency-curve is narrow and simple, 
and has a single summit. The shaft of these spicules is straight, cylindrical, 
18-30 » thick, usually 20-26 u, and thickened at or near the middle of its length 
to a central tyle 4-12 » more in transverse diameter than its adjacent parts. 
Several broad, terminally rounded spines 3-8 » long arise from the central 
tyle. The remaining parts of the shaft are smooth. 
The terminal anchors are 55-78 uw in length, usually one sixth to one fourth 
of the whole spicule, and 105-140 » broad. The proportion of their length to 
their breadth is 100 to 155-236, on an average 100 : 174.3. The individual 
teeth attain their maximum breadth of 20-30 u in their distal part, and are very 
abruptly pointed, the contour of their end-part having, when seen en face, the 
shape of a broad gothic arch. The teeth are uniformly curved; the outer con- 
tour of the anchor when seen in profile is generally nearly semicircular. 
The serrated macramphidiscs (Plate 107, figs. 1-5, 17-20) are 150-328 yu long. 
Their length frequency-curve is rather broad and irregular, and has three distinct 
summits. The middle one is quite insignificant; the other two, situated at about 
164 and 240 u respectively, are very pronounced. The shaft of these amphi- 
dises is straight, 3-6 » thick, and thickened at or near the middle of its length 
to a central tyle 2-6 » more in transverse diameter than its adjacent parts. 
The central tyle bears a verticil of cylindrical, terminally rounded, straight or 
curved spines 5-14 u long. The remaining parts of the shaft are covered with 
numerous low protuberances (very short spines). 
The terminal anchors are 61-105 » long, the whole spicule being 2.5 to 3.5 
times as long as the anchor. The maximum anchor-breadth is 45-100 ». The 
end-parts of the teeth of some of these anchors are nearly parallel; in these anch- 
ors the end-breadth is equal to the maximum breadth; the end-parts of the 
teeth of others are convergent,— in these anchors the end-breadth is 2-6 yu less 
than the maximum breadth. The proportion of anchor-length to anchor-breadth 
is 100 to 72-102, on an average 100 : 83.6. 
The individual teeth arise vertically from the shaft, are strongly bent in 
their basal part, and straight or only slightly curved in their distal part. Their 
tips are, as mentioned above, parallel or slightly convergent. The teeth attain 
their maximum breadth of 12-15 u in their middle-part, and are attenuated 
