228 Dr. G. J. Hinde—Spicules in Archeocyathus. 
places on their outer surfaces small rounded granules like those of 
Beekite. The fragments are in part porous, and several of them 
are filled with fragmentary spicules dispersed irregularly in the 
rock, and apparently in various stages of dissolution. In the finer 
débris are smaller particles of silica and detached entire and broken 
spicules. From these I have picked out fairly complete fusiform 
acerate spicules (Fig. 1, 6, c, d), acuate or pin-shaped spicules (a), 
and portions of nearly cylindrical forms (e). The spicules are of 
chalcedonic silica, and their axial canals are preserved in many 
instances. They are common types of siliceous monactinellid 
spicules, and belong to at least four species of sponges. Forms 
of a similar character, and similarly detached, are very abundant 
in the cherty beds of the Yoredale rocks of Yorkshire. I have 
but little doubt that these siliceous fragments from the Mingan 
strata, in which Archceocyathus occurs, have been produced by the 
dissolution of the spicules of disintegrated monactinellid sponges, 
and the redeposition of the silica as Beekite. 
I have not, however, detected in the débris examined a single 
fragment of the so-termed ‘branching spicula’ (Fig. 1, f—7), described 
and figured by Billings as forming part of the substance of the outer 
wall of A. Minganensis. Judging from the figures given of them, I do 
not think they can be regarded as spicules; they are merely abruptly 
broken fragments of what appears to have been a delicate continuous 
porous membrane; no two of them are similar, and they do not bear 
any definite resemblance to any sponge spicules with which I am 
acquainted. I have no doubt that—as stated—they form part of 
the outer wall of Archeocyathus Minganensis, but instead of being 
‘branching spicula,’ they are merely broken portions of the 
calcareous tissue of the outer wall, replaced by silica. ‘The structure 
of the outer wall in the allied species A. Whitneyz, Meek, is described? 
as consisting of minute punctures so closely crowded that the little 
divisions between them are scarcely equal in breadth to the 
punctures themselves, and form, as it were, an extremely delicate 
kind of network, and the so-termed ‘branching spicula’ in A. 
Minganensis might well be broken-up portions of a network of this 
character. 
Therefore as regards the true sponge-spicules associated with 
A. Minganensis, it is evident there is no other connection between 
them and this species than the accident of position, and the so- 
termed branching spicula, which really belong to this fossil, are in 
all probability mere siliceous replacements of the tissue of its outer 
wall. ‘Thus in neither case is there any evidence in support of the 
view that Archeocyathus is allied to siliceous sponges. My know- 
ledge of this puzzling fossil is insufficient for me to give a competent 
Opinion as to its real nature; it is fairly certain, however, that its 
skeleton was originally calcareous, and it is just possible that careful 
microscopical examination might give a clue to its relations. 
1 American Journ. Sci. vol. xlv. p. 62. 
