256 
HYALONEMA (PRIONEMA) AGUJANUM. 
The stout- and short-rayed proximally smooth mon- to pentactine acanthophores 
(Plate 76 , figs. 8-16, 31, 32). The pentactine forms (Plate 76 , fig. 32) are rare 
and have been found only in var. tenuis, form A. They are very much smaller 
than the others and may perhaps be spicules of another kind. The tetractine 
forms (Plate 76 , figs. 8, 10-13) with four fairly equally developed rays are 
frequent in all the specimens. Their rays extend in the same plane and enclose 
angles of 90°. They are usually straight and attenuated towards the end. 
The triactine forms are not nearly so frequent. They are evidently tetractine- 
derivates and differ from the true tetractines only by one ray being much reduced 
or suppressed altogether. Transitions between the tetractines and triactines 
(Plate 76 , fig. 10) are by no means rare. The diactine forms (Plate 76 , figs. 14- 
16) are frequent. They sometimes possess, besides the two properly developed 
rays, a rudiment of a third ray (Plate 76, fig. 15). Those without such a rudiment 
are either centrotyle and spindle-shaped (Plate 72 , fig. 14), or simply cylindrical 
and rather thicker at the ends than in the middle (Plate 76 , fig. 16). The mon- 
actines (Plate 76 , fig. 31) are rare. They appear as tylostyles. The dimensions 
of these spicules are the following: — 
Only terminally spined, basal spicules with 
4 3 2 1 
Hyalonema 
(Piionema) more or less fully developed rays 
agujanum 
maximum 
diameter 
(length) m 
thickness of 
rays ju 
maximum 
diameter 
(length) ft 
thickness of 
rays m 
maximum 
diameter 
(length) m 
thickness of 
1 rays m 
maximum 
diameter 
(length) £i 
thickness of 
| rays ai 
maximum 
diameter 
(length) m 
thickness of 
rays m 
var. tenuis 
form A 
45 
6 
167- 
240 
14-17 
230- 
295 
17-18 
117- 
320 
11-21 
194 
21 
form B 
140- 
440 
11-28 
275- 
340 
15-20 
570- 
1400 
10-20 
190 
17 
var. lata 
350- 
530 
12-14 
870 
12 
all forms and 
varieties 
14 
6 
140- 
530 
11-28 
230- 
870 
12-20 
117- 
MOO 
10-21 
190- 
194 
17-21 
As the entirely spined short-rayed basal acanthophores are sufficiently 
abundant for proper study and measurements only in the Palythoa, and as only 
