HYALONEMA (HYALONEMA) AGASSIZI. 
193 
first elevation of the curve of form D corresponds to still shorter amphidiscs, of 
about 180 /d in length. The curves of forms A, D, and F have a small secondary 
elevation at about 290 n. The curve of form B has a secondary elevation at 
about 164 n] the curve of form F has also an additional slight secondary eleva- 
tion at about 112 /*. 
These curves indicate that A, E, and F have, on the whole, smaller large 
macramphidiscs than the other forms; that D possesses two nearly equally 
numerous varieties of these spicules, a larger and a smaller one; and that in C 
the small forms of the large macramphidiscs are much rarer than in the others. 
They further show that the large macramphidiscs of all the six different forms 
differ in respect to the character and range of the variation of their length. It is 
also to be noted that none of the curves are similar to a mathematical proba- 
bility curve; for these spicules do not, in respect to their length, vary uniformly 
round a mean. 
The small macramphidiscs of form A (Plate 46, fig. 1) are 62-115 p long, 
most frequently about 93 n, and have a cylindrical centrotyle shaft 3-8 n thick. 
The central thickening bears a verticil of rather blunt spines 1.3-1. 5 n long and 
about 0.5 fx thick. Numerous similar spines are found on the other parts of the 
shaft. The anchors are 22-43 m long, that is about a third, generally a little 
more than a third, of the whole spicule, and are 16-42 n broad. The proportion 
of their length to their breadth, in the smaller forms under 80 n in length is, 100 to 
73-84, on an average 100 : 79; in the larger forms, over 80 n in length, it is 100 to 
76-105, on an average 100 : 90. The shape of the individual anchor-teeth is, 
on the whole, similar to that of those of the large macramphidiscs; but it is to be 
noted that their curvature, in the smaller forms of these spicules, is considerably 
greater. 
In the specimen of this form (A) I found a remarkable hexactine spicule 
116 n in diameter, composed of four fully developed and two rudimentary rays. 
The four developed rays are cylindrical, 7.5 n thick, and bear at their ends verticils 
of large recurved teeth which together form somewhat irregular anchors 36 n 
long and about 64 n broad. One of the rudimentary rays is a short, terminally 
rounded cylinder; the other is bifurcate and slightly longer at the end. The 
whole spicule appears as a cross formed by two small macramphidiscs joined 
in the middle, from the centre of which two protuberances arise. 
Spicules of this kind have occasionally, but very rarely, been observed in 
other species of Hyalonema, as H. tenerum. 1 The only hyalonematid in which 
1 F. E. Schulze. Rept. Voy. Challenger, 1887, 21, pi. 31, fig. 18. 
