Mr. II . J. Carter on the Hexactinellidae. 303 



Short Commentary on the Hexactinellid.e. 



As considerable difference exists between the older and 

 youngest portions of the vitreous Hexactinellida3, it is necessary 

 for specific distinction that fragments from both should be ex- 

 amined — first in their natural state, and then after boiling for 

 a few moments in nitric acid or liquor potasste; while the 

 minute spicules of the sarcode, viz. the rosettes &c, which 

 come off in the boiling, should, with any minute fragments of 

 the skeleton that may remain, be well washed, dried, and 

 mounted in Canada balsam for examination with a hia:her 

 power. 



The chief difference in structure between Dactylocalyx 

 pumiceus, Stutchbury, and the following specimen, viz. D. 

 pumicea, Gray, is that the latter is charged, especially 

 towards the surface, with long linear spicules (slender, fusi- 

 form, slightly inflated and spined for some distance at each 

 end), while there are none to be seen in D. pumiceus. 



I say "none" advisedly, because I have repeatedly sought 

 for them in the type specimen of D. pumiceus without success. 

 Boiling in nitric acid completely frees D. pumiceus and D. 

 pumicea from the rosette, because the rosette belongs entirely 

 to the sarcode ; but the long acerate spicule, although it also 

 appears to be isolated, is retained in the latter by its bent 

 position in the vitreous structure, thus fixing it there by its 

 elasticity; so that, if these spicules had been equally common 

 in D. pumiceus, S., each fragment should contain portions of 

 them, as in D. pumicea, G. Had not Dr. Bowerbank figured 

 the central (and thus unmeaning) portion of one in his illus- 

 trations of the type specimen of D. pumiceus (I. c.) without the 

 most distant allusion to such spicules in his description, I 

 should not have thought it necessary to write so much 

 about it : as it is, I am compelled to the conclusion not only 

 that such a spicule does not exist in D. pumiceus, but that 

 Dr. Bowerbank has, as in other instances, introduced it as part 

 of the illustrations of this species by mistake (to wit, the 

 surface-spicule of MacAndrewia azorica with his illustration 

 of Myliusia callocyaihes, P. Z. S. 1869, pi. xxiii. fig. 6). 



Independently, however, of this difference (and the rosette, 

 which, although alike in other respects, is a little more robust 

 in D. pumicea than in D. pumiceus), I find it so impossible, 

 either in the general form of the specimens of these two sponges 

 or in their reticulated structure respectively, to see the self- 

 evident facts which should determine a specific distinction, 

 that I can hardly consider them varieties, much less different 

 species, as Dr. Bowerbank has made them. 



