76 GEODIA JAPONICA. 



more or less curved rhabdome, 3.3-4.3 mm. long, and at the cladome, 8-16 fi 

 thick. At its acladomal end it is usually attenuated to a fine, often consider- 

 ably and irregularly curved thread (Plate 38, figs. 29, 30). Exceptionally the 

 rhabdome is somewhat shortened and thickened to a tyle at the acladomal 

 end. The clades arise at an angle of about 80° from the rhabdome. In very 

 young anatriaenes, such as the one with clades only 20 /t long represented in 

 Plate 38, fig. 18, the clades arc uniformly curved, concave to the rhabdome 

 throughout their entire length. This curvature not being great, however, the 

 chords of the clades of such young anatriaenes enclose angles of over 50° with 

 the axis of the rhabdome. During the further development the direction of 

 growth undergoes a change, the silica being thenceforth apposed to the growing 

 clade in such manner that its tip becomes a straight, slender, and sharp-pointed 

 cone, strongly inclined to the rhabdome and enclosing with it an angle of only 

 about 20°. The further growth of the clade may go on in the same tlirection: 

 tlion clades with straight distal parts arc formed (Plate 38, figs. 19-22); or there 

 may be a continuous change in a direction ojjposite to that of the curvature 

 of the proximal part : then clades with distal ends curved outward are formed 

 (Plate 38, figs. 23-29). This cui-vature gives, when well i)ronounccd (Plate 38, 

 figs. 28, 29), a sigmoid appearance to the clades. The anatriaenes with such 

 sigmoid clades are very characteristic of this sponge. The chords of the clades 

 of the full-grown anatriaenes are 80-130 /£ long and enclose angles of 23-41°, 

 on an average 32.2°, with the axis of the rliabdome. The anatriaenes have, 

 according to Sollas, a rhabdome 18 /« thick and clades 100 /i long. According 

 to Thiele the anatriacne-clades arc 70 /t long. The remarkable outward curva- 

 ture of the ends of the clades of many of the anatriaenes is indicated in Thiele's 

 figure but is not mentioned in the text either by him or by Sollas. In the type 

 of Sollas examined by me a few anamonaencs of similar dimensions besides the 

 regular anatriaenes were found. The latter have a rhabdome 2.4-5 mm. by 

 11-23 /«, clades 70-110 /i long and clade-angles of 32-45° on an average 36.7°. 

 The minute dermal anaclades (Plate 39, figs. 13c, 14-17, 38, 39) have a more 

 or less curved rhabdome, 235-310 /i long and rounded at the acladomal end. 

 At the cladome the rhabdome is 1-2 /i, in its thickest part, which usually lies 

 below the middle, 2.8-5 fx, and at the rounded, acladomal end 1.3-3 /i thick. 

 The proportion of the thickness of the cladomal end to the thickest part to the 

 acladomal end is, on an average, 10:28: 17. I have observed triaene, diaene, 

 and monaene forms. The clades are always curved, concave to the rhabdome; 

 their length is very variable. The chords of the clades are 3-10 fi long and 



