52 



SIDONOPS BICOLOR. 



thickness of the rays and, apart from the one-rayed forms, also the total diameter 

 of the aster are roughly in inverse proportion to the ray-number. In the rare 

 one-rayed form the centrum is 5 in diameter, and the ray 18 fi long and 5 n 

 thick at the base. The oxyasters with from three to five rays measure 28-34 n, 

 the oxyasters with six or more rays 19-29 j« in total diameter. The oxyasters 

 of the specimens from Station 4531 are slightly smaller than those of the others. 



DIMENSIONS AND NUMBER OF RAYS OF OXYASTERS. 



Stations 



2958 



2981 



3168 



4420 



4531 



4551 



Total diameter /x 



24-33 



22-34 



23-34 



20-32 



19-28 



22-33 



Diameter of centrum /i 



3.3-4.2 



3-6 



3.5-4 



2.8-5 



3-4,5 



3-5 



Basal thickness of lays /< 



1.3-2.3 



1.5-2.8 



2-3 



1.5-5 



1-2.5 



1 . 6-2 . 5 



Numljer of rays 



7-8 



6-10 



3 9 



1.5-10 



4-12 



3-12 



The oxysphaerasters (Plate 11, fig. 7b) have a spherical centrum 4.5-10 fi 

 in diameter, from which from twelve to twenty-five rays arise radially. The 

 rays are concentric, distributed regularly, 0.7-2.5 /j. thick at the base, conical, 

 straight, and pointed at the end. The distal part of each ray, usually about the 

 distal half of it, is covered with spines. Not infrequently a group of somewhat 

 larger spines, arranged in a more or less verticillate manner is situated a short 

 distance below the end of the ray. In the centrifugal spicule-preparations of the 

 specimen from Station 2958 I found several oxysphaerasters with rays entirely 

 destitute of spines, otherwise similar to the ordinary ones. These may possibly 

 be foreign to the sponge. In total diameter the oxysphaerasters measure 10-23 

 /.(. The largest ones pass into the oxyasters described above. The oxysphaer- 

 asters of the specimens from Stations 4531 and 4551 have on the whole more 

 rays than those from other stations, and specimens with more than twenty rays 

 have been observed only in the specimens from these stations. 



DIMENSIONS AND NUMBER OF RAYS OF OXYSPHAERASTERS. 



Stations 



2958 



2981 



3168 



4420 



4531 



4551 



Total diameter /< 



14.5-21.5 



17-21 



19-23 



14-18.5 



14-16.5 



10-19 



Diameter of centrum /i 



4.5-10 



6-7.5 



6-7 



5.5-7 



6-6.5 



4-7.5 



Basal thickness of rays /i 



1-2.5 



1.5-2 



1-2.5 



1.5-2.5 



1.5-2 



0.7-1.8 



Number of rays 



12-16 



14-18 



14-17 



14-17 



19-23 



19-25 



