HYALONEMA (HYALONEMA) AGASSIZI. 
191 
average 100 : 103. The anchor-teeth are T-shaped in transverse section. The 
upper part appears as a curved band, for the greater part of its length 8.7-11.5 n 
broad, and attenuated to a point or, more rarely, rounded off at the end. The 
teeth arise steeply and are uniformly curved, concave to the shaft. The curva- 
ture is not very great and never suffices to give the end-parts of the teeth a 
direction parallel to the shaft. The tangents on these end-parts enclose, in the 
adult large amphidiscs, angles of about 5° with the axis of the shaft. In young 
spicules of this kind (Plate 46, fig. 9) this angle is, of course, much greater. 
The large macramphidiscs of form B (Plate 46 , fig. 15) are 126-310 /x long, 
most frequently about 240 fx. Their shafts are 8-14 m thick, and their anchors 
are 46-67 /x long and 48-76 /x broad. These spicules are longer and have smaller 
anchors than those of form A. 
The large macramphidiscs of form C (Plate 46 , figs. 10, 11) are 110-290 n 
long, most frequently about 240 n. Their shafts are 6-10 n thick, and their 
anchors 40-63 /x long and 35-75 /x broad. They are very similar to those of 
form B, and are like them longer and provided with smaller anchors than those 
of form A. 
The large macramphidiscs of form D (Plate 46 , figs. 6-8, 16) are mostly 
regular and similar to those of the other forms. They are 132-282 n long, most 
frequently either about 240 or 180 n, with shafts 9.5-12 n thick, and with anchors 
52-73 m long and 48-66 /x broad. In respect to their length the regular large 
macramphidiscs of form D are intermediate between forms B and C on the one 
hand and form A on the other. Their anchors are similar in size to those of 
forms B and C. In the specimen of form D I found an irregular large macram- 
phidisc (Plate 46 , fig. 7) 192 /x long, with a shaft 4.4 /x thick. The two anchors 
of this spicule are both about 26 /x broad but very unequal in length, one being 
44 n long, the other considerably shorter. The shaft is beset with numerous 
large pointed spines, all strongly bent towards one end. These spines increase 
in size towards the end from which they diverge; the largest is 16 n long. 
The large macramphidiscs of form E are 150-280 n long, usually 170-256 n, 
most frequently about 200 fx. Their shaft is 6-12 /x thick. Their anchors are 
51-67 ix long and 51-80 /x broad. 
The large macramphidiscs of form F are 112-260 m long, usually 150-232 n, 
most frequently about 200 n. Their anchors are 36-65 ix long and 34-70 m 
broad. In a preparation of one of the specimens of this form I found an ab- 
normal large macramphidisc, in which the central spine- verticil was replaced 
by an anchor similar to but slightly smaller than the terminal anchors. 
