HYALONEMA (HYALONEMA) AGASSIZI. 193 



first elevation of the curve of form D corresponds to still shorter amphidiscs, of 

 about 180 M in length. The curves of forms A, D, and F have a small secondary 

 elevation at about 290 fjt. The curve of form B has a secondary elevation at 

 about 164 m; the curve of form F has also an additional slight secondary eleva- 

 tion at about 112 yu. 



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- 

 biUty curve; for these spicules do not, in respect to their length, vary uniformly 

 round a mean. 



The small viacramphidiscs of form A (Plate 46, fig. 1) are 62-115 n long, 

 most frequently about 93 /x, and have a cylindrical centrotyle shaft 3-8 /x thick. 

 The central tliickening bears a verticil of rather blunt spines 1.3-1.5 fi long and 

 about 0.5 ju thick. Numerous similar spines are found on the other parts of the 

 shaft. The anchors are 22-43 ix long, that is about a third, generally a Httle 

 more than a tliird, of the whole spicule, and are 16-42 fi broad. The proportion 

 of their length to their breadth, in the smaller forms under 80 fi in length is, 100 to 

 73-84, on an average 100 : 79; in the larger forms, over 80 fi 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 yu 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 m 

 long and about 64 fj. broad. One of the rudimentary rays is a short, terminally 

 rounded cyhnder; 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} The only hyalonematid in which 



' F. E. Schulze. Kept. Voy. Challenger, 1887, 21, pi. 31, fig. IS. 



