til the Environs of Brussels. 387 



Lamarck states of AsperfjiUnm (tliat is, upon the fraf^mcnts of 

 A. vaginiferum brou-z;!!! home from the lied Sea by Savigny), 

 that " II doit avoir pkisieurs picds de longueur " (' Anim. sans 

 VertJibres,' ed. 1818, voK v. p. 430). 



Fossil sponge-spicules. — The fossil sponge-spicules so well 

 selected and represented in the plate accompanying M. Rutot's 

 excellent paper [op), et loc. cit.) are, for the most part, in a 

 detached and fragmentary state, consisting of an indefinite 

 number of kinds and forms from as many different sponges, 

 mixed up with the tests of minute Foraminifera, fragments of 

 minute Echinodermata, the disks of Diatomacea;, and grains 

 of quartz-sand, all of which occupies the intervals between 

 the pisiform eminences of the tuberculous layer and between 

 their summits respectively and the concretionary crust — that is, 

 coats the former generally (fig. 8, c), — the tuberculous layer 

 itself, as before stated, having been observed, where still adhe- 

 rent to the central cylinder (fig. 6 i), to be composed of the same 

 quartzite material as the latter. Hence the mixture of spi- 

 cules &c., which is nearly the same in each " tubulation " (as 

 I have ascertained by examination, having carefully kept that 

 belonging to each separate), must have been gathered up by 

 the surface of the tuberculous layer, and that, too, with a par- 

 tiality for such material, as it does not exist so plentifully in 

 the deposit in which the tubulation is imbedded, as testified 

 by the composition of the concretionary crust. At the same 

 time, as the accumulation of spicules &c. must have been 

 going on more or less ^;ari passu with the growth of the 

 tuberculous layer, the latter might also have been more or less 

 composed of such material. 



To describe the sponge-spicules in detail (which, being 

 detached in the friable material, are easily picked out with the 

 point of a hair-pencil) would occupy more time than I now 

 have at my disposal ; and therefore I shall premise the few 

 observations I may have to make on them generally with the 

 statement that, after repeated efforts, I have not been able to 

 find anything more important in this respect than is contained 

 in the plate accompanying M. Rutot's paper ; hence constant 

 allusion will be made to his figures. 



Hexactinellida. Among the fragments of the siliceous 

 skeletons of the Vitreohexactinellida there are, at least, two 

 forms (Rutot, pi. iii. figs. 31-34), one of which is nmch more 

 abundant than the rest ; and this presents the lantern-like or 

 octahedral form of the knot of Myliusia Grayi (' Annals,' 

 1877, vol. xix. pi. ix. fig. 10, &c.), but so far different that 

 the fibre between the knots is microspincd, and the spines, 

 instead of being scattered irregularly over the fibre as in M. 



