HYALONEMA (HYALONEMA) AGASSIZI. 183 
The hexactine megascleres of form A (Plate 45, figs. 6-13) measured were 
0.4—6 mm. in maximum diameter. The rays of the same spicule are in the smaller 
ones either equal or unequal, in the largest ones always unequal in length, two 
opposite ones being in these much longer than the other four. The four shorter 
rays are often also unequal among themselves. The rays arise from a central 
thickening 30-90 u in diameter, are smooth, conic, 10-58 uw thick at the base, 
and blunt or rounded at the end. They are in the small hexactines straight, 
in the large usually slightly curved. The longest ray is 220 »-3.2 mm. long. 
The hexactines of forms C and D are similar. In form B I found, besides 
hexactines similar to those of form A, one 11 mm. in maximum diameter with 
rays 70 » thick at the base, and only slightly attenuated to the rounded ends. 
In this form also spined hexactines, 2-5.5 mm. in diameter, occur. Although 
these are quite numerous and found in the depth of the choanosome, I do not 
believe that they really belong to the sponge. They are, like the large spined 
pentactines referred to above, identical with the spined hexactine and pentac- 
tine megascleres of Calycosilva cantharellus (Plate 1, figs. 5-24; Plate 6, figs. 1-12), 
a large number of specimens of which were trawled at the same station. Some 
of the spined hexactines and pentactines of these sponges may therefore have got 
accidentally into the sponge. 
In the basal part of the body, from which the stalk arises, slender acantho- 
phores, usually with four, more rarely with five or six rays (Plate 42, figs. 49, 51— 
59), are met in all the forms except E and F. Inform A these spicules (Plate 42, 
figs. 49, 51, 52) are 95-170, usually 110-135 yu in diameter, and generally consist 
of four rays lying in the same plane and enclosing angles of 90° with their neigh- 
bours. Sometimes a fifth ray, vertical to the other four, is present. The rays 
of these spicules are fairly straight, at the base 2.5—4 u thick, rarely 5 u, conic, and 
sharp-pointed. They bear numerous slender oblique spines inclined towards 
the tip of the ray. The largest spines are 4-12 u long. 
In form B these spicules (Plate 42, figs. 53, 54) are similar, measure 85-150 » 
in diameter, and have rays 2-4.5 thick at the base. Here only tetractines were 
observed. 
In form C these spicules (Plate 42, figs. 55, 56, 58) are larger, 120-210 yu in 
diameter, and have four or, more rarely, five fairly straight or considerably 
curved rays, 3.5-5 u thick at the base. 
In form D some of these spicules (Plate 42, figs. 46, 57, 59) attain a still 
larger size. They measure here 100-230 » in diameter and have usually five, 
more rarely four or six rays 2.8-6 « thick at the base. 
Transitional forms were found quite frequently in the basal part of the 
