20 



SIDONOPS CALIFORNICA. 



The minute, dermal styles are usually slightly curved, 175-290 fjt long and in 

 the central parts 3-7 n thick. They taper slightly towards the proximal rounded 

 end. The distal end is sharp pointed. 



The minute microa?nphioxes which may be foreign to the sponge, and possi- 

 bly form dragmes, are quite straight, about 50 fi long and Ipt thick. 



The orthoplagiotriaenes (Plate 5, figs. 13-19) have a rather small clade-angle 

 and might therefore perhaps also be termed orthotriaenes. The rhabdome 

 is straight, conic, and usually sharp pointed, rarely blunt. It is 0.9-1.45 mm. 

 long and at the cladomal end 20-78, usually 35-55 /i thick. I do not think that 

 the great differences in the thickness of the rhabdome, which are clearly notice- 

 able in comparing the spicules represented in figures 13 and 18 on Plate 5, can 

 be altogether ascribed to differences in their age. The clades are 160-400 ^ long, 

 conic, often rather blunt, and uniformly curved, concave to the rhabdome. 

 Their chords enclose angles of 104-120° with the axis of the rhabdome. The 

 three clades of the same cladome often differ in size and sometimes exhibit a 

 sagittal character. 



The anatriaenes (Plate 5, figs. 1-4) have long and more or less curved 

 rhabdomes, which are 10-17 /< thick at the cladomal end. The clades are rela- 

 tively stout and 22-45 /< long. Their proximal part is quite strongly curved, 

 their distal part straight. Their chords enclose angles of 45-66° with the axis 

 of the rhabdome. A slight apical knob is usually discernible on the summit of 

 the cladome. 



Anatriaene-derivates of similar dimensions with two clades (anadiaenes) 

 (Plate 5, fig. 5) and one clade (anamonaenes) also occur, but they are rare. 

 The branched end of a very peculiar spicule, which may be an anatriaene- 

 derivate, is represented in fig. 10 on Plate 5. This spicule is a rhabd with two 

 small, recurved, clade-like branches, arising a little below one of the pointed 

 ends, and a very large straight branch-ray, also pointing downwards and en- 

 closing an exceedingly small angle (about 4°) with the rhabdome, arising some 

 distance below the small branch-rays. 



The mesoplagioclades (Plate 5, fig. 7-9) have a long rhabdome which is, 

 just below the clades, 6-15 /i thick. The epirhabd is conic and 45-125 long. 

 The number of clades is one (Plate 5, fig. 7), two (Plate 5, fig. 9) or three (Plate 

 5, fig. 8). The clades are nearly straight, pointed or rounded at the end, and 

 20-42 n long. They are directed obliquely upwards and their axes enclose 

 angles of 102-118° with the axis of the rhabdome. These plagioclade spicules 

 replace the mesoprotriaenes of other geodine sponges, and I am inclined to 



