128 Mr. H. J. Carter on Fossil Sponge-spicuhs of 



Before returning to the ternate system again, I may here 

 briefly allude to two other kinds of spicules, not in this dej^osit, 

 called respectively by Dr. Bowerbank " biternate " and " tri- 

 furcated attenuato-hexradiate " spicules, the former belong- 

 ing io Dactylocalyx subghhosa^ Gray (Proceed, cit. 1869, pi. 22. 

 hg. 11), and the latter to Eiqjiectella aspergillum (Brit. Spong. 

 pi. 8. fig. 189), since the straight lines in fig. 34 are introduced 

 to show how these two forms might be produced. Viewing, 

 then, those marked a « a as branches of the axial canal, 

 producing the ternate system, we have the lines hah, hah, 

 and h ah with the shaft in the centre, forming Dr. Bower- 

 bank's "biternate" spicule; and by adding another branch 

 with hah, so as to produce the quadrifid head, together wdtli 

 one above and one below in the axis of the shaft, we get the 

 " trifurcated attenuato-hexradiate " form. But as these forms 

 are only to be found among the minute spicules of the existing 

 species to which they respectively belong, they do not come 

 into the category with which w^e are most concerned, although 

 it seemed desirable to give them a passing notice. Again, it 

 should be remembered, as enlarged figures often mislead, that 

 if the spicules in question were draw^n to the scale of our figure 

 34, under reference, their utmost size would not be more than 

 the semidiameter of the circle representing the broken end of 

 the shaft ; hence their subordinate nature in respect of size. 



It is very desirable, where we can, to take our characters 

 rather from large than smallobjects; for it is much more usefid to 

 the many, who cannot afford to purchase microscopes for seeing 

 the latter; and it becomes questionable how far species-split- 

 ting should be subject to microscopical examination, since 

 there might be no end to this if there were no limit to micro- 

 scopic power : hence the desirableness of restricting the latter 

 in the formation of species, even as it is, to some practicable 

 extent. 



Beturning to the ternate system of the large fossil spicules 

 with long shafts, we have, in figs. 32, 35, & 36, PI. IX., 

 heads only, in which the shafts although not represented, are 

 known to have been long; also figs. 59 to 71, inclusively, in 

 PI. X., Avhcre the heads and fragments of their long shafts 

 still remaining together are thus represented. 



And here, directing our attention first to the furcate division 

 of the arms, or the hexternate forms in figs. 32, 34, and 35, 

 PI. IX., and figs. 58, 59, 60, QQ, & 68, PI. X., we observe 

 that, altliough there is great irregularity in their dividing, 

 they are all jjrovided with long shafts. (Again I must beg the 

 reader to remember that these figures are not selected from 

 their rarity, but as the best representatives that I could find 



