106 LANUGONYCHIA FLABELLUM. 



The (hypodermal and hypogastral) pentadines (Plate 13, figs. 10, 12, 13, 

 16b) have an apical (proximal) ray 0.6-1 mm. long, and lateral (paratangential) 

 rays 400-800 /x. The lateral rays of the same spicule are more or less unequal, 

 the longest usually being 150-250 m longer than the shortest. All the rays are 

 straight, conic, blunt, and 20-40 yu thick at the base. The end-parts of the 

 lateral rays bear quite numerous sharp-pointed spines. Proximally these spines 

 become more blunt, lower, and less numerous, and they pass gradually into 

 slight, hardly perceptible, flattened protuberances, finally disappearing alto- 

 gether. The proximal parts of the lateral rays are smooth. 



Pentadines with very long apical rays (Plate 13, figs. 9, 16a) have also been 

 observed. The apical (proximal) ray is in these spicules 3-9 mm. long. The 

 lateral rays are usually broken; one intact one (Plate 13, fig. 9) was 1.85 mm. 

 long and curved. These spicules may be foreign. Some of them are strongly 

 corroded. 



A few large sword-like hexadines with the rays of one axis differently devel- 

 oped from the rays of the other two axes have also been observed. The two rays 

 in the differentiated axis represent the blade and the handle of the sword. The 

 former is very long and broken off in the spicules observed. The latter is 165 m 

 long and covered with spines. At the base it is 24-30 n thick and either cylindri- 

 cal or terniinally thickened, club-shaped. The other four rays, which represent 

 the guard of the sword, appear to be long and ec|ual among themselves. They 

 were all broken off in the sword-like hexactine observed. These spicules seem 

 to take part in the formation of the skeleton of the stalk ; it is possible, however, 

 that they are foreign. 



The small hexadines and hexadine-derivates (Plate 12, figs. 24-34; Plate 13, 

 figs. 5c, 28) always have fairly straight rays, but are, apart from this, remarkably 

 variable and irregular. In the first place the angles between adjacent rays are 

 not, as is generally the case in hexactinellid spicules, invariably 90°. In a good 

 many of the tetractine (stauractine) (Plate 12, fig. 33), the triactine, and particu- 

 larly the diactine (Plate 12, fig. 26; Plate 13, fig. 5c) forms, other than right 

 angles are enclosed by them. This angular irregularity is particularly pro- 

 nounced in some diactines which appear as variously opened compasses (Plate 12, 

 fig. 26; Plate 13, fig. 5c). In the second place one to five of the rays may be 

 reduced to mere terminally rounded protuberances arising from the centre of 

 the spicule. Finally the reduced rays and, to a certain extent, also the fully 

 developed rays of the same spicules are frequently unequal among themselves. 

 In spite of this variability there are, however, absolutely no transitions between 

 the reduced and the properly developed rays. 



