210 
HYALONEMA (HYALONEMA) PLACUNA. 
The lateral rays of the same spicule are usually all alike. They are 25-42 n 
long, attenuated distally, in their basal part very gradually, in their distal part 
abruptly, and pointed at the end. Sometimes one (Plate 64 , fig. 8, to the left) 
or more (Plate 64 , fig. 8, to the right) of them are reduced in length, only 20-24 n 
long, nearly cylindrical, and rounded at the end. The lateral rays are smooth, 
or provided with a few small spines. 
The dermal pinules of form B (Plate 64 , figs. 9, 10, 17- 19) differ from those 
of form A chiefly in the maximum thickness of their distal ray, together with the 
spines, which is situated farther up, nearer to the tip of the ray. These pinules 
are not, as those of form A appear to be, all pentactine, but some hexactines 
occur among them. The distal ray of these spicules is 385-458 m long, most 
frequently 399-445 and 7-11 m thick at the base. The terminal cone is 
usually 18-27 n long. The maximum thickness of the distal ray, together with 
the spines, is 35-62 m, most frequently 40-60 /j. The proportion of the length of 
the distal ray to the distance between the point of maximum thickness (together 
with the spines) and the centre of the spicule (the base of the distal ray) is 100 to 
71-86, most frequently 100 to 76-84, on an average 100 : 79.6. The lateral rays 
are 28-44 ^ long. The proximal ray of one of the hexactine forms is 34 ^ long. 
The ordinary gastral pinules of form A are nearly always pentactine, very 
rarely hexactine. In form B pentactine forms only were observed. The distal 
ray of the ordinary gastral pinules of form A (Plate 65 , figs. 19-21) is straight 
or, rarely, angularly bent and 153-390 m long, usually 200-360 n. It is somewhat 
spindle-shaped, thickest at a point about one third of its length from the base. 
At the base it measures 7-12 n, at the thickest point 10-16 m, in thickness, and it 
ends in a rather long and slender terminal cone. Its distal and its proximal end- 
parts are spineless. The remainder of it bears rather sparse and distant spines. 
The lower spines arise steeply or vertically from the ray and then curve upwards, 
often very markedly, towards its tip (Plate 65 , fig. 21 ). The upper spines for their 
whole length are strongly inclined and slightly curved towards the tip of the ray. 
They decrease in size distally, the uppermost ones being very small. The maxi- 
mum thickness of the distal ray, together with the spines, is usually 30-38 u, 
rarely less, down to 22 The lateral rays are 37-85 m long, usually 40-70 n, 
conic, and pointed. They are in the distal half, or two thirds of their length, 
beset with somewhat sparse, conspicuous, vertical or outwardly directed spines. 
A good many of the pentactine forms of these spicules possess a large spine oppo- 
site the distal ray. This spine may be a rudiment of the proximal ray. In the 
rare cases where the sixth (proximal) ray is properly developed, it attains a length 
of 27-73 M . 
