OF THE SPONGIAD^. 253 



Fig. 



rare occurence, without a slight iudication near the 

 middle, of the absent" third and fourth rays of the 

 perfect cruciform spiculum, 



157. Spiculated cylindbo-crtjciform. X 174 linear. — 



Prom Hyalonema mirabilis, Gray, British Museum. 

 This spiculum is from the sheath of the same 

 sponge as those represented by Figs. 153 to 156. 

 The ordinary cruciform spiculum being converted 

 into an external defeiisive one by the projection of 

 a spicular ray from its centre. 



158. Attenuato-stellate. X 660 linear. — Having the 



radii gradually attenuated from the base to the 

 apex. Fachymatisma Johnstonia, Bowerbank, 

 affords a large and very excellent type of this form 

 of spiculum. The radii vary from three to seven 

 or eight, but five or six rays are the most common 

 numbers. Page 51. 



159. Cylindro-stei^late, from Fachymatisma Johnstonia, 



Bowerbank. X 660 linear. — Having the radii of 

 nearly equal diameter throughout, and terminating 

 hemispherically. This form also occurs abundantly 

 in Tethia robusta, Bowerbank, MS. The sponge is 

 in the British Museum, and was brought from 

 Australia by Mr. S. Stutchbury. The form and 

 proportions of these spicula vary considerably; 

 sometimes the distal terminations of the radii are 

 slightly inclined to be clavate, and at others there 

 is a gradual transition from simply stellate to sub- 

 sphero-stellate. The radii are also in some of the 

 larger specimens slightly inclined to attenuation. 



160. Ceassato - CYLINDRO - STELLATE. X 1060 linear. — 



This spiculum is remarkable from its having the 

 radii twice as broad as they are thick, and their 

 distal terminations abruptly truncated. It occurs 

 intermixed with the more regular forms of cylindro- 

 stellate in Tethea robusta. 



