HYALONEMA (HYALONEMA) AGASSIZI. 195 



In form D, where they are also rather frequent, the large micramphidiscs 

 (Plate 45, figs. 63, 64) measure 35-55 ;u in length, most frequently about 47.5 n. 

 Their shafts are spiny and 1.5-1.7 ^ thick; their anchors are shorter than in the 

 other forms, 15-17 fi long, and 10-11 n broad. 



In the specimens of form E the large micramphidiscs are exceedingly abun- 

 dant. They are here 40-69 n long, most frequently about 48 n, and have anchors 

 13-21 M long and 8-14 ti broad. 



In the specimens of form F the large micramphidiscs are not nearly so 

 numerous. They are here 37-57 n long, most frequently about 52 m, and have 

 anchors 14-20 m long and 9-14 m 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 fornis A, B, C, 

 and E. The small inicramphidiscs 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 inicramphidiscs. 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 yu long, most frequently about 18.3 n. 

 The limit between the larger and the smaller kind lies at about 29 ju. The shaft 

 is straight or rarely bent, 0.6-1.4 n thick, cyhndrical 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 /x long, or it is covered 

 with sparse, \'ertical, more rarely oblique, spines throughout. The anchors are 

 4-13 fi long, that is a quarter to a third of the whole spicule, and 4.7-9 n 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 



