GEODIA JAPONICA. 



75 



domal end is usually blunt pointed, rarely rounded and slightly thickened. 

 The clades are, when normally developed, stout, conic, usually blunt pointed, 

 and 180-350 long. Their basal part is slightly curved, concave to the rhabd- 

 ome, their distal part straight. Their chords enclose angles of 90-102°, on an 

 average 96.4°, with the axis of the rhabdome. The orthotriaene forms (with 

 clade-angles 90-100°) greatly predominate, the plagiotriaene forms (with clade- 

 angles over 100°) forming only about 15% of these spicules. The clades 

 of the same cladome are, in the normally developed triaenes, usually rather 

 unequal in length. In the normal cladome (Plate 37, fig. 17), the three 

 clades measured 250, 300, and 340 /<. Sometimes one, two, or all three clades 

 are considerably reduced in length, cylindrical and rounded terminally. Ac- 

 cording to Sollas these spicules have a rhabdome 2.4-2.6 mm. by 78 and 

 clades 230-380 ii long; according to Thiele a rhabdome 2.5 mm. by 50-60 /x, 

 clades 200-300 /t long, and clade-angles of 92°. In Sollas's type I found these 

 spicules had a rhabdome 2.3-2.9 mm. by 50-70 //, clades 200-300 /( long, and 

 clade-angles of 93-100°, on an average 95.5°. 



The mesoproclades (Plate 38, figs. 9-17) have a rhabdome 2.8-4.3 mm. long 

 and 11-21 jj. thick at the cladomal end. At the acladomal end the rhabdome 

 thins out to a slender, irregularly curved thread. The cladomes are variable, 

 irregular forms with partly reduced clades predominating over the regular 

 mesopro triaenes. The epirhabd is usually straight, conical, sharp pointed, and 

 40-105 [J. long. Sometimes (Plate 38, fig. 16) it is shortened, rounded at the end, 

 and curved, rarely reduced to a mere knob on the apex of the cladome. The 

 clades are, when properly developed, conical, pointed and 65-125 // long. Their 

 basal part is curved, concave to the epirhabd, their distal part straight (Plate 38, 

 figs. 9, 11, 17) or curved in the opposite direction (outwards) (Plate 38, figs. 12, 

 15). An abrupt angular bend often intervenes between these two parts. In the 

 majority of these spicules one or two clades are more or less reduced in length, 

 cylindrical, and terminally rounded (Plate 38, figs. 15, 17). Sometimes this 

 reduction has gone so far that one, two, or all three clades appear as mere knobs 

 (Plate 38, figs. 11, 13, 16) or are altogether absent (Plate 38, fig. 12). The 

 chords of the clades enclose angles of 22-48°, on an average 34°, with the axis 

 of the epirhabd. In young mesoproclades (Plate 38, fig. 14) not only are the 

 epirhabd and the clades shorter but also the clade-epirhabd angles much greater. 

 Mesoproclades or proclades are not mentioned as occurring in this sponge either 

 by Sollas or by Thiele, neither could I find any in the type of the former. 



The large anatriaenes (Plate 37, figs. 29, 30; Plate 38, figs. 18-29) have a 



