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 ^ in diameter, are smooth, conic, 10-58 m thick at the base, 

 and blunt or rounded at the end. They are in the small hexactines straight, 

 in the large usually slightly curx-ed. The longest ray is 220 ;u-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 /x 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, Uke 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. In form A these spicules (Plate 42, 

 figs. 49, 51, 52) are 95-170, usually 110-135 m 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-^ m thick, rarely 5 m, conic, and 

 sharp-pointed. They bear numerous slender oblique spines inclined towards 

 the tip of the ray. The largest spines are 4-12 fi long. 



In form B these spicules (Plate 42, figs. 53, 54) are similar, measure 85-150 n 

 in diameter, and have rays 2-4.5 m thick at the base. Here only tetractines were 

 observed. 



In form C these spicules (Plate 42, figs. 55, 56, 58) are larger, 120-210 ^ in 

 diameter, and have four or, more rarely, five fairly straight or considerably 

 curved rays, 3.5-5 m 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 m 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 



