Siliceous Spicules of Sponges. 213 



In Carteria there is a very extraordinary form of the sex- 

 radiate spicule, which, in its perfect state, has six short arms 

 of nearly equal length, each arm ending in a series of four or 

 eight elongate oblong reflexed radiating lobes. Dr. Bowerbank 

 only represents this form of spicule, which he calls " multi- 

 dentate birotulate spicule " (B. S. t. iii. f. 62), as simple with 

 the lobes at each end ; and Dr. Schultze (Hyalonema, t. iv. 

 f. 11, 12) has figured the same rudimentary spicule; but Mr. 

 Carter has found it perfectly developed into six rays, and dif- 

 ferent specimens with the lateral rays more or less perfectly 

 developed, some with terminal radiating lobes, and others with 

 the arms reduced to mere conical processes, as may be seen in 

 Dr. Schultze's figure. 



Schultze, in his ' Hyalonema,' figures a minute spicule having 

 four short recurved conical arms at each end (t. iv. f. 10) ; 

 and Bowerbank (B. S. t. v. f. 122) figures this spicule, which 

 he says is " dispersed in considerable abundance in the inter- 

 stitial membrane " of Carteria, and calls it " quadrihamate 

 spicule;" but this spicule, I suspect, from the spinules on its 

 stem, is very probably only an imperfect state of a sexradiate 

 spicule, like the one which Bowerbank calls " birotulate," 

 having only four lobes instead of many. 



Mr. Carter figures a very minute birotulate spicule of this 

 kind occurring in Corticium abyssi (Ann. & Mag. Nat. Hist. 

 1873, xii. t. i. f. 7). In Echinospora there is a solid octa- 

 hedral spicule, each of the six angles produced into a cylindrical 

 ray dentated at the end ; this is found with two flat three- 

 rayed stars placed one on the other, figured in the ' B. Sponges,' 

 t. x. f. 197 (see Ann. & Mag. Nat. Hist. 1870, vi. pp. 272 & 

 340). Dr. O. Schmidt, in his 'Atlantic Sponges,' t. ii. f. 16, 

 figures a hollow octahedral formed by marginal tubes, and 

 having six diverging rays. 



5. The multiradiate or stellate spicules have five or more 

 rays, arising and diverging from a common centre or very 

 short axis, as the stellate spicules figured by Bowerbank (B. S. 

 t. vi. f. 158-161) found along with the spherules in Pachyma- 

 tisma and Tethea. (See also Bowerbank, P. Z. S. 1872, 

 t. xlvi.-xlviii., and 1873, t. i.-iii. Schmidt, ' Sponges,' t. iii. 

 f. 22, 26, t. iv. f. 1, 2, 4, t. v. f. 1 ; < Algiers,' t. iii. f. 2, 4, 

 t. iv. f. 5, 6, 8, Suppl. t. v. f. 5. Carter, Ann. & Mag. Nat. 

 Hist. 1867, iv. t. i. & ii.) 



Probably the candelabrum-like spicule (Schmidt, Spongienf. 

 t. iii. f. 25) should also belong to this series. 



There are very probably many more forms to be referred to 

 this type ; but all this will require much more study than I 

 am able to bestow upon the subject. (See B. S. t. vi. f. 164, 165, 



