318 
HYALONEMA (OONEMA) B I AN CHORATUM PINULINA. 
The rare monactine and frequent diactine rhabd-forms are in specimen a 
270 m- 1-3 mm. long and 17-37 m thick, on an average 25.4 /x ; in b 145 ix-\A mm. 
long and 9-40 n thick, on an average 16 n. The more slender ones, 20 u or less 
thick, are, in both specimens together, 420 id-lA mm. long, the stouter ones, over 
20 n thick, only 270-740 /j. long. The rare triactine and frequent tetractine 
forms are in specimen a 120-420 n long, with rays 20-44 n thick, on an average 
31 /d] mb they are 110-500 n long, with rays 12-34 n thick, on an average 22.4 /x. 
The pentactine and hexactine forms, both of which are not numerous, are in 
specimen a 180-350 /x long, with rays 15-24 n thick; in b they are 80-390 n 
long, with rays 8-25 n thick. 
The rays of the tri- to hexactines usually differ in length more or less, often 
very considerably. The rays of the tri- and tetractines always extend in one 
plane, whilst the pentactine and hexactine forms resemble, in respect to the 
position of their rays, the pentactine and hexactine megascleres above described. 
The rays are more or less, exceptionally (Plate 82 , figs. 11, 12) very considerably, 
curved and nearly always simple, very rarely branched (Plate 82 , fig. 17). They 
are cylindrical or cylindroconical, not infrequently somewhat uneven, and 
rounded and usually thickened at the end. The terminal thickenings are 
particularly well-developed in the rhabd-forms, and these usually also have a 
central tyle. In a fairly typical diactine spicule of this kind, 1 mm. long and 
16 /d thick, the central tyle is 18 n in transverse diameter, and the terminal 
tyles 30 /x and 34 ^ respectively. The central tyle is either well-defined (Plate 
83 , fig. 5) or not (Plate 83 , fig. 1). In all the larger and a good many of 
the smaller basal spicules, the proximal and middle-parts of the rays are 
smooth, apart from the occasional slight undulations of their surface. The 
end-parts are nearly always densely spined, or exceptionally smooth (Plate 82 , 
figs. 19, 20, 34). A good many of the smaller basal spicules (Plate 82 , figs. 10, 
18, 28-30) are entirely spined, the spines on their proximal parts being usually 
slightly smaller than those on their distal parts. The entirely spined forms are 
much more frequent among the basal spicules of specimen a than among those 
of b. The spines are broad and conical. Those measured were 2-6 n long, 
rarely up to 10 id. 
The spicules forming the skeleton of the Palythoa attached to the stalk of 
specimen a (Plate 83 , figs. 36-44, 46-59) are monactine to tetractine. The 
rare monactine and frequent diactine rhabd-forms are 122-520 n long and 
20-40 ii thick, on an average 32.4 n. The rare triactine and frequent tetractine 
forms are 90-290 n long and 20-40 n thick; the average thickness is 31.6 n. 
