HYALONEMA (HYALONEMA) GRANDANCORA. 



237 



The hexadines (Plate 79, figs. 13-19) are 0.4-3 mm. in diameter, and have 

 nearly equal or somewhat unequal, conical and pointed, straight or slightly 

 curved rays 10-80 ^ thick at the base. 



The rhabds are centrotyle, generally more or less curved, 0.8-1.3 mm. long 

 and 10-20 n thick. The central tyle is 1-3 m more in transverse diameter than 

 the adjacent parts of the spicule. 



Among the acanthophores the diactines and tetractines are much more 

 frequent than the others. In the entirely spined forms the rays are shorter and 

 thicker than in the ones with rays spined only terminally. The dimensions of 

 these spicules are the following: — 



In the rod-shaped monactines and diactines which are only terminally spined 

 an inverse proportion between length and thickness is clearly pronounced : — 

 the spicules of this kind 154-400 ju long are 26-41, on an average 29.7 fx thick 

 " " " 401-550 IX " " 19-26, " " " 22.5 m " 

 " " " 551-1100 M " " 10-23, " " " 15.2 m " 

 The entirely spined spicules of this kind exhibit a similar relation between 

 length and thickness: — 



those 85-120 m long are 35-58, on an average 43.3 m thick 

 " 121-290 M " " 28-31, " " " 29 m " 

 The long and slender diactines which are only terminally spined have a 

 central tyle 2-8 m more in transverse diameter than the adjacent parts of the 

 spicule. In some of the shorter and stouter ones the tyle is relatively larger. 

 The spines are broad and conical. In the entirely spined forms they are usu- 

 ally about 7 IX, very rarely as much as 10 ix, long and broad; in those with rays 

 only terminally spined they are smaller. 



Besides these spicules a few pinule-like, entirely spined pentaciine and 

 hexactine acanthophores with one differentiated ray were found in the basal 

 l^art of the sponge. The dimensions of these spicules, which I consider as pinule- 



