318 HYALONEMA (OONEMA) BIANCHORATUM PINULINA. 



The rare monactine and frequent diactine rhabd-forms are in specimen a 

 270 ;u-1.3 mm. long and 17-37 ix thick, on an average 25.4 yu; in 6 145 ^-1-4 mm. 

 long and 9-40 ix thick, on an average 16 n. The more slender ones, 20 n or less 

 thick, are, in both specimens together, 420 ^-1-4 mm. long, the stouter ones, over 

 20 II thick, only 270-740 ^ long. The rare triactine and frequent tetractine 

 forms are in specimen a 120-420 ^ long, with rays 20-44 m thick, on an average 

 31 yu; in h they are 110-500 yu long, with rays 12-34 ^ thick, on an average 22.4 m- 

 The pentactine and hexactine forms, both of which are not numerous, are in 

 specimen a 180-350 ^ long, with rays 15-24 yu thick; in h they are 80-390 m 

 long, with rays 8-25 yu 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 M thick, the central tyle is 18 n in transverse diameter, and the terminal 

 tyles 30 n and 34 n 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 h. The spines are broad and conical. Those measured were 2-6 yu long, 

 rarely up to 10 m- 



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 yu long and 

 20-40 M thick, on an average 32.4 yu. The rare triactine and frequent tetractine 

 forms are 90-290 /x long and 20-40 yu thick; the average thickness is 31.6 m- 



