210 Dr. J. E. Gray on the 



istic of Tethyadte are sometimes found with well-developed 

 quinqueradiate spicules (see Schmidt, Suppl. t. iii. f. 8). 



Mr. Carter figures a beautiful modification of this spicule 

 found in Corticium abyssi, which has branches at the ends of 

 the lateral rays. The lower end of the axis and the lateral 

 rays are crenated on the sides (see Ann. & Mag. Nat. Hist. 

 1873, xii. t. i. f. 3-6). 



Dr. Bowerbank, in his representation of the spines of the 

 very young Tethya cranium, represents the long clasping spi- 

 cules as having only one hook, on one side, at the end (B. S. 

 t. xxv. f. 343). Mr. Carter has well observed that this is a 

 " monstrous representation " (Ann. & Mag. Nat. Hist. 1872, ix. 

 p. 420, t: 20) ; and at p. 430 (t. xxii. f. 16) he gives four repre- 

 sentations showing how the one-armed spicule gradually de- 

 velops into a three-rayed one, and (f. 17) the variations of 

 shape that occur, and that the spicules belong to the quinque- 

 radiate form, and (in t. xxii. f. 3) how the axis is sometimes 

 produced beyond the lateral spicules. 



Bowerbank (B. S. t. ii. f. 41 & 42) figures a curious spicule, 

 which appears to have three diverging trifid rays on each end 

 of a very short broad axis, and may be a reduplication of this. 

 Indeed B. S. fig. 197 may also be something of the same 

 kind, but with a shorter axis ; probably B. S. fig. 69 may be 

 a series of branched rays arising from a cylindrical axis. 

 B. S. figs. 199 & 200 may be modifications, of the same kind, 

 of double series of three simple or branched rays arising from 

 two centres of the axis ; but these modifications have not 

 occurred to me. 



4. The sexradiate spicules form a large group. They consist 

 essentially, in the most simple and perfect state, of an elongated 

 axis giving out from the centre of its length four equidistant 

 arms diverging at right angles from the axis, as in B. S. t. vii. 

 f. 184, 185. 



The various modifications of this spicule have been well 

 shown by Schultze in his essay on Hyalonema, t. iii. & iv. 



Bowerbank figures several variations in B. S. t. vii. f. 184- 

 195, as they occur in different parts of Alcyoncellum. Some- 

 times 1, 2, 3, or all the lateral arms are wanting; in others, 

 as fig. 183, the four lateral arms are complete, and one arm of 

 the axis is wanting ; but Bowerbank gives to each of these 

 spicules a different name. 



The sexradiate spicules are abundant and of the usual form 

 in Carteria, the sponge that grows parasitic on the top of the 

 glassrope (Hyalonema) from Japan ; but when this sponge 

 occurs, as it sometimes does, under the bark of the Hyalonema, 

 then the spicules seem to change their character. Instead of 



