156 BRITISH SPONGIADJ}. 



complications the regularly compacted primary lines 

 of the skeleton, however devious their courses may 

 be, unmistakably characterise the normal structure of 

 an Isodictya ; when a careful scrutiny of its structural 

 peculiarities is effected. The complication of the ske- 

 leton structures is also much increased by the irre- 

 gular mode of disposition of the large attenuato-acuate 

 spicula, the office of which appears to be really subsi- 

 diary to the true skeleton spicula amidst which they 

 are irregularly disposed, among both those of the 

 primary and secondary series. These spicula have all 

 the structural appearances of large internal defensive 

 organs; they vary to a considerable extent in size, 

 some of the largest being twice as long as the smallest 

 ones, but the basal portions appear to be all of nearly 

 the same size ; but notwithstanding these deceptive 

 appearances, none of them were found erect and pro- 

 jected into the interstitial cavities of the sponge after 

 the mode of the usual disposition of defensive spicula, 

 but on the contrary, they all appeared to be prostrate 

 among the spicula of either the primary or the secon- 

 dary series of the skeleton lines ; and not unfrequently 

 a single one might be observed fulfilling the office of a 

 secondary or connecting spiculum between two of the 

 lines of the primary skeleton structure. They are 

 very much stouter than those of the true skeleton 

 spicula, and are very numerous. The basal ends of 

 these spicula are abundantly spinous, and the spines 

 are strongly produced, terminating hemispherically, 

 while the spines of the shaft for about half the length 

 of the spiculum become gradually less in size until 

 they are at last in quite an incipient state. 



" This remarkable sponge cannot readily be mistaken 



