GEODIA MESOTRIAENA. 



107 



dimensions these spicules agree with the regular anatriaenes described above. 

 The epirhabd of the mesanatriaene of var. megana, Plate 23, fig. 13, is 200 /jl long. 



DIMENSIONS OF ANATRIAENES OF GEODIA MESOTRIAENA. 





Var. pachana 



Var. megana 



Var. microana 



Rhabdome 



length mm. 



11-16 



15 



11 



thickness at the 

 cladome fi 



27-40 



22-38 



8-25 



Clade-chords length /i 



90-170 



160-270 



70-175 



Angles between clade- 

 chords and axis of the 

 rhabdome 



maximum and 

 minimum ° 



39-56 



34-58 



39-55 



average ° 



48.2 



45.2 



47.9 



Among the normal euasters which occur in great numbers, small strongylo- 

 sphaerasters, small and large oxyasters with small centrum or without centrum, 

 and large oxysphaerasters can be distinguished. Besides these a few large 

 strongylosphaerasters are found. These aster-forms are connected by numerous 

 transitions. 



The oxijasters (Plate 24, figs, lb, 6b, 7a, 9b, 10-14a, 15, 19, 22, 23, 24a, b, 

 25a, b, 26 31) are 11-54 /x in total diameter. They have a relatively small 

 centrum, the diameter of which is from one eleventh to one seventh of the total 

 diameter of the spicule, or no central thickening at all. Their rays are concentric, 

 straight, and conical. In some of these asters the rays are in their proximal parts 

 nearly cylindrical and decrease in thickness with increasing rapidity towards 

 the distal end (Plate 24, fig. 23). In others the rays are more regularly conical 

 and attenuated quite uniformly from base to tip (Plate 24, fig. 25a). The end 

 of the ray is usually blunt pointed, not so frequently either sharp pointed or 

 truncate. The basal part of the ray is smooth, the distal part, rarely also 

 smooth (Plate 24, fig. 26), usually covered with a varying number of smaller or 

 larger spines (Plate 24, figs. 27-31). The u. v. photographs (Plate 24, figs. 28- 

 31) show that these spines arise vertically and that they are often recurved 

 towards the centre of the spicule, in a claw-shaped manner. These oxyasters 

 have from five to twenty rays. Small oxyasters 11-20 /< in diameter with from 

 nine to twenty rays, and large oxyasters 19-54 /j. in diameter with from five to 

 fifteen rays can be distinguished. The largest oxyasters, that is those over 40 fx 

 in diameter, have from six to eleven rays, while the smallest oxyasters have 



