418 On Calcareous Hexactinellid Structure, dc. 
what have been supposed to be the remains of Calcispongiz, 
from their triradiate appearance and calcareous composition 
(Grantia antiqua, Moore, Quart. Journ. Geol. Soc., Dec. 1867, 
p. 538, pl. xvi. figs. 33, 34). They are white, and all frag- 
ments of quadriradiate forms—that is, spicules composed of 
a trifid head and shaft, to me very much like the quadri- 
radiates of Pachastrella abyss, Sdt.; but be this as it may, 
among them was a head and part of the shaft of a trifur- 
cate spicule which must have belonged to a siliceous sponge 
(Geodia or Stelletta), im the same condition of fossilization 
as the rest—that is, calcareous. I took a fragment of one 
from the parent rock, and having placed it in a little dilute 
nitric acid, saw it effervesce, and at last break down into 
minute particles ; while Mr. Moore informs me that he treated 
some with hydrochloric acid, and they all disappeared. 
Now it is very natural that trifid forms of sponge-spicule 
should be taken for those belonging to the Calcispongie, 
especially if they are calcareous ; but it should be remembered 
that while there are very few Calcispongiz which possess 
triradiates or quadriradiates sufficiently large to pass through 
the ordeal of fossilization without disappearing altogether, 
there are many Pachastrellida which possess both forms much 
larger than the largest of any that are known to exist in the 
Calcispongie ; while the possibility of the siliceous spicule 
becoming calcareous during fossilization has, as above stated, 
been established. 
Thus we may find separate sponge-spicules of the siliceous 
sponges and whole siliceous sponges themselves calcified; but 
it would not be right to call these “‘ Calcispongie:” even 
“ Calcificatee ’? would be better than this. 
With reference to the chalcedonized Pachastrellida and 
their spicules in the Chalk, I have now two beautiful speci- 
mens that appear to have been freed from the latter by an 
acid, each of which is from 3 to 4 inches in its longest diameter, 
one irregularly lobate, and the other vase-shaped, where the 
quadriradiate spicules, simple and trifid at the ends of their 
arms respectively, are identical with those of Pachastrella 
abysst, Sdt., while they are so confusedly thrown together, 
and the mass thus rendered so characteristically asperous, that 
it is impossible to see in them any thing but a Pachastrella. 
Here too, in many parts, the trifid heads are alone visible, 
which might be easily taken for those of a Calcisponge—espe- 
cially as Pachastrella, like the Calcisponge, being without that 
fibrous structure which entails regularity in the distribution 
of its spicules, appears to be entirely without arrangement of 
the latter; so that in this respect each looks like a bag of pins. 
