GEODIA MICROPORA. 



173 



7) are observed. The clades are rather blunt, sometimes nearly truncate, and 

 curved towards the rhabdome. In the basal part of the clade this curvature is 

 very considerable; distally it decreases, and the ends of the clades are only 

 slightly curved or even quite straight. The clades rise at rather large angles 

 from the rhabdome, but, in consequence of their strong curvature, their chords 

 enclose angles of only 97-112°, on an average 104.5°, with the axis of the rhabd- 

 ome. The greater number of these spicules appear as plagiotriaenes (with 

 clade-angles over 100°), about 20 % of them as orthotriaenes (with clade-angles 

 90-100°). The chords of the clades are 175-240 n long. 



The cladomal end of the axial thread of the rhabdome is often varicose and 

 in some of the young orthoplagiotriaenes a slight thickening of the rhabdome 

 surrounds this part of the axial thread. 



In the spicule-preparations I found several chelotrops (Plate 37, figs. 10, 11). 

 These have conical, pointed, usually straight, more rarely angularly bent rays, 

 195-260 p. long and, at the base, 21-27 fj. thick. I have not found any of these 

 spicules in situ in the sections. Although they coincide in their dimensions with 

 the orthoplagiotriaenes, I think it probable that they are foreign to the sponge. 



The mesoproclades (Plate 36, figs. 13-17) have a rhabdome about 1.7 mm. 

 long and, at the cladome, 4-9 pt thick. In its central part the rhabdome is 

 about 20 % thicker than at the cladome. The shape of the cladome is very 

 variable. The epirhabd is usually well developed, straight, conical, pointed, and 

 25-43 /I long. Sometimes it is quite short, reduced to a mere knob. Of clades 

 there may be three (Plate 36, fig. 13), two (Plate 36, fig. 16), or one (Plate 

 36, fig. 17). In the monaene forms knob-shaped rudiments of one or two 

 other clades, usually situated at different levels, are often present (Plate 36, 

 fig. 14). The clades are conic pointed or blunt, and curved, concave to the 

 epirhabd. Their chords are 10-30 /< long and enclose angles of 32-64°, on an 

 average 51°, with the epirhabd. 



The large oxyasters (Plate 36, figs. 24-26d, 34b) are without central thickening 

 and have from six to nine, most frequently seven, concentric, regularly distributed 

 rays. The rays are straight, conic, 8-12 jn long, and very slender, at the base, 

 only 0.4^.9 p., usually 0.6-0.7 /t thick. Everywhere, except at the base, they 

 bear small spines. Towards the end the ray proper becomes exceedingly thin ; 

 the spines, however, which are here particularly dense, make its terminal part 

 appear thicker and its end somewhat blunt. The total diameter of the oxyasters 

 is 14-20 fi, usually 16-17 p. 



The large oxysphaerasters (Plate 36, figs. 18b, 19b, 26c, 33b) have a spherical 



