372 Mr. H. J. Carter on the Hexactinellidai. 



the spicule disappears under the parasitic polype (Palithoa 

 fatua) which afterwards, for some distance down, covers the 

 cord like a bark. Finally, the spicules again make their ap- 

 pearance, but now with the spines gone and the bracket-like 

 processes alone remaining in the form of a rough more or less 

 continuous spiral line round the spicule, which, together with 

 the free extremities of the smooth anchoring-one, also are 

 always broken off, so that their free terminations are gone : this 

 is the state in which these spicules appear for the most part 

 in the trade specimens. 



I have now described the anchoring-spicules of the specimen 

 of Hyalonema above mentioned, whose body is about 1^ inch 

 long ; and throughout the spicule, all the spines and blunt ends 

 of the bracket-like processes both within and without the body 

 are directed upwards — that is, towards the sponge at the summit 

 of the cord. 



Had I not been misled by the observations of others to regard 

 the mounted specimen of the young Holtenia Carpenteri u half 

 an inch long " in the first place as a young Hyalonema, the 

 mistake to which I have above alluded would not have occurred. 

 But finding it out, and having therefore had to examine more 

 particularly these anchoring-spicules in an undoubted specimen 

 of Hyalonema, I am enabled not only to correct the error, but 

 to add more authentic information on the subject than was pre- 

 viously possessed, as well as to point out decisive marks for 

 distinguishing between young Holtenue and young Hyalone- 

 mata another time. 



The transition from the sparsely spined anchoring-spicule of 

 Holtenia Garpenteri through that of Meyerina clavijbrmis to 

 that of Hyalonema is represented inPl. XIV. figs. 7, 8, & 9, where 

 also a comparative view of the heads or free terminations of 

 the anchoring-spicules of Labaria kemisphcerica (figs. 1 & 2), 

 Meyerina clavijbrmis (fig. 3), Euplectella (figs. 4 & 5), and 

 Holtenia Carpenteri (fig. 6) is also given, to which I have 

 alluded in the " Observations " appended to my description of 

 Labaria ( l Annals/ vol. xi. p. 280, &c, 1873). 



Holtenia Carpenteri, Fheronema Annce, P. Grayi, and Meye- 

 rina claviformis all probably possess the same kind of birotulate 

 spicule as Hyalonema (PL XIII. fig. 21). I say " probably " 

 with reference only to Prof. Leidy's hasty description of this 

 sponge, in which this spicule appears to have been overlooked. 

 As in Hyalonema, so also probably in all the other Hexacti- 

 nellidas characterized by the birotulate flesh-spicule, this is not 

 unfrequently found in a sexradiate form, which at once iden- 

 tifies it with the rosette (fig. 22) ; that is, it may consist of three 

 birotulates joined together in the centre, and thus present six 



