126 Mr. H.J. Carter 07i Fossil Sponge-spicules of 



Thus the hextemate head seems to take us from the Pachy- 

 tragije of the shore through the Coralliospongias of the com- 

 paratively shallow seas, clown into the deep recesses of the 

 ocean, where, at 1913 fathoms, Dr. Wallich found the dimi- 

 nutive but important little sponge to which Dr. Wright [1. c.) 

 has given the name WyviUe-Thomsonia Wallichu. Already 

 it will have been seen that M. de Pom-tales found this (for 

 Stelletta {Tisiplionia) agariciformis of Schmidt appears, mut. 

 mutand.^ to be identical with it) in 178 fathoms ; so that here 

 we have a sponge, in form and habitat respectively, connecting 

 the Pachytragije of the shore, through the Coralliospongise, 

 with the Calycispongiffi (Kent) of the deepest seas. 



Figs. 37, 38, and 39, Plate IX., and figs. 72, 73, and 74 

 PI. X., are nail-like spicules, whose crucial or fom--anned heads 

 as plainly show that they do not belong to the ternate as that 

 they do belong to a quaternate or quadiifid system, whose 

 parallel, as before stated, is only found in the spicules of Hy- 

 alonema {CaHeria, Gray). 



On this, however, it may be observed that the minute 

 spicules with feathered shafts and quadrifid heads are not con- 

 fined to Hyalonema^ but are found also in Holtenia Caipenteri, 

 W. Thomson (Phil. Trans. 1869, pi. Ixviii. figs. 9-11), and 

 in Pheronema Grayi^ Kent (Monthly Microscop. Journ., Nov. 

 1870, pi. Ixiii. figs. 9 and 10). So are there minute hexra- 

 diatc spicules in many of the Coralliospongia3 and Euplectel- 

 lida3 ; but Dr. W. Thomson states, respecting the former, 

 that " opposite to the point of junction of the vertical with the 

 four transverse rays there is frequently a more or less distinct 

 rounded elevation or tubercle. This undoubtedly represents 

 the sixth ray, the continuation of the pnmary axis of the spi- 

 cule" (PhiL Trans. 1869, p. 704); so that these feathered 

 shafts with quadiifid heads in Holtenia evidently belong to 

 the hexradiate system. But v/here Dr. W. Thomson goes 

 on to state that in some cases " the tubercle is developed into 

 a branch, and the spicule becomes hexradiate, recalling the 

 ordinary hexradiate spicule of the sponge-mass oi Ilyalonema^'' 

 I must join issue, inasmuch as I have never been able to see 

 such a tubercle in the minute spicules with feathered shafts 

 and quadrifid heads, nor in the large quadi-ifid spicules of 

 Hyalonemcij although examined carefully for this purpose ; nor 

 have I ever seen in any illustrations, or in my own examina- 

 tion of my mounted specimens of the sponge of liyalonema^ 

 any 7/ea;radiate spicules ; while, as before stated, the simple 

 cross in the centre of the longer spicules, which was first 

 pointed out by Schultze (Ann. /. c), has always appeared to 

 nic </;/ar7/-<(radiate, as stated l)y him, and not /^^^an-adiate with 



