HYALONEMA (HYALONEMA) AGASSIZI. 
195 
In form D, where they are also rather frequent, the large micramphidiscs 
(Plate 45 , figs. 63, 64) measure 35-55 ^ in length, most frequently about 47.5 ij. 
Their shafts are spiny and 1.5-1. 7 ij thick; their anchors are shorter than in the 
other forms, 15-17 n long, and 10-11 n broad. 
In the specimens of form E the large micramphidiscs are exceedingly abun- 
dant. They are here 40-69 m long, most frequently about 48 ij, and have anchors 
13-21 ij long and 8-14 ^ broad. 
In the specimens of form F the large micramphidiscs are not nearly so 
numerous. They are here 37-57 m long, most frequently about 52 /x, and have 
anchors 14-20 /j long and 9-14 ^ broad. 
According to the frequency of those of different length, three kinds of small 
micramphidiscs can be distinguished in form F, and two kinds in forms A, B, C, 
and E. The small micramphidiscs of form D are all of the same kind. The 
smaller (A, B, C, E) or smallest (F) kind is invariably the most abundant. The 
spicules belonging to the larger (A, B, C, E) or largest (F) kind have very slender 
anchors and appear as transitions between the (broad-anchored) small and the 
(slender-anchored) large micramphidiscs. Judged morphologically, by their 
shape alone, the larger (largest) kind of small micramphidiscs should, indeed, 
be considered as belonging to the large micramphidiscs. Since, however, in 
the smaller (A, B, C, E) or smallest and intermediate (F) kinds of small micram- 
phidiscs the relative breadth of the anchors decreases with the increase in 
the size (length) of the spicules, since in a few exceptional spicules of this kind 
the anchors are quite as slender as in the larger (largest) kind, and since they are, 
in the forms where they occur, separated biometrically much more clearly from 
the larger micramphidiscs than from the smaller kind of the small micramphi- 
discs, I provisionally place them in the latter group. 
The small micramphidiscs of form A (Plate 44 , fig. 17d; Plate 45 , figs. 40- 
45; Plate 47 , figs. 3, 4, 7-9) are 15-36 /j long, most frequently about 18.3 /j. 
The limit between the larger and the smaller kind lies at about 29 The shaft 
is straight or rarely bent, 0.6-1. 4 /j thick, cylindrical throughout, or slightly and 
gradually thickened in the middle. It is either quite smooth, or it bears near 
the centre an irregular cluster of a few spines, not over 0.5 /j long, or it is covered 
with sparse, vertical, more rarely oblique, spines throughout. The anchors are 
4-13 m long, that is a quarter to a third of the whole spicule, and 4.7-9 ^ broad. 
They consist of fifteen or sixteen recurved teeth. In the larger kind of small 
micramphidiscs the proportion of the length to the breadth of the anchor is 
100 to 58-75, on an average 100 : 64; in the smaller kind 100 to 75-135, on an 
