LANUGONYCHIA FLABELLUM. 



107 



These hexactines and hexactine-derivates measure 134-318 /x in total 

 diameter. Their fully developed rays are 83-180 fj. long and 5-14 ju. thick at the 

 base. They are usually regularly conic and sharp-pointed, rarely cyhndro- 

 conic and somewhat blunt. The reduced rays are 6-25 yu long, 7-16 ^ thick, 

 cyhndrical, and terminally rounded. The length and thickness of the properly 

 developed rays is, as the subjoined table shows, in the monactine to pentactine 

 forms in inverse proportion to their number. The hexactine forms apparently 

 do not conform to this rule. Since, however, the state of preservation of the 

 specimen renders it impossible to ascertain clearly whether the not numerous 

 larger hexactines are choanosomal or superficial, it might be assumed that these 

 large hexactines are choanosomal spicules and do not belong to the series repre- 

 sented by the dermals and gastrals, to which that rule applies. The small 

 hexactines conform to the rule, and some at least of these are certainly superficial. 



HEXACTINES AND PENTACTINE TO MONACTINE HEXACTINE-DERIVATES. 



Pully developed rays 



Both the fully developed and the reduced rays are covered with spines. 

 On the basal parts of the fully developed rays the spines are somewhat sparse 

 and here they arise vertically. On their distal parts the spines are more numer- 

 ous and here they point obliquely outward. The extreme tip of the ray is 

 usually free from spines for a distance of 4 or 5 fi. The spines are conic, sharp- 

 pointed, and 0.5-2 n high. Their size is in proportion to the thickness of the ray 

 from which they arise, the stoutest rays bearing the largest spines. 



The cylindrical, terminally rounded, more or less knob-like, reduced rays 

 are covered with similar spines, which are either smiilarly distributed as on the 

 fully developed rays or more crowded. 



