File:The Quarterly journal of the Geological Society of London (12895019843).jpg

1864..
SALTER LINGTTLA-FLAG FOSSILS.
239
which the branches are arranged in more than
one plane, and hence there is no danger of
confounding the Primordial form with those
Silurian genera*.
There are many unpublished Spongiadse
from true Silurian Bocks t

and it is at least
satisfactory to find that these had their ante-
cedents in a formation whose much greater
antiquity is now well established. The fauna
of the Lingula-flags is even yet a scanty one.
In some few of its genera it shows an ap-
proximation to Lower Silurian forms

and
some Shells and a Cystidean are of genera
common to both formations. But the Crus-
tacea here, as elsewhere in the Pakeozoic
rocks, are our surest indices of age

and the
entire distinctness of the Trilobite fauna
overbalances the fact that species of Orthis,
of Distinct, of Theca, and of Trochocystites are
found both in Silurian strata and in the great
Primordial formation which lies near the base
of the fossiliferous rocks of "Wales. With the
exception of Agnostus and Leperditia, not a
single Crustacean genus is known to pass from

In a letter from Dr. Bowerbank, to whom I sent
specimens of Protospongia, he refers to his recent
genus Spongionella (Phil. Trans. 1862, plate 74. fig.
10) as the nearest ally. The pyritized state of the
fossil favours the view which he takes, that this is
one of the true horny sponges allied to the genus
just quoted, sponge-fibre decomposing but slowly.
The remains here figured are not, in Dr. Bower-
bank's view, the spiculae, but the sponge-fibre itself
replaced by pyrites

and, if so, the size of the fibres
would be nothing remarkable, since it maybe paralleled
in many recent species. While I do not share Dr.
Bowerbank's opinion (I believe these are true spiculae),
I feel bound to give his authority for a contrary view,
the more so as there seem to be several Silurian and
other palaeozoic forms which may be better explained
in this way, such as Ischadites, Tetragonis, &c. The
remarkable genus Arch.20cyathus, Billings (Geology of
Canada, pp. 283, 285, 286), described in 1861, has no
relation to our fossil, and was probably calcareous.
There is, I think, much doubt if the limestones there
described truly belong to the Primordial group, though
included with the Potsdam Sandstone. Eospongia,
published in the same year, does not need com-
parison.
t I may mention here that a fine species of Astylo-
spongia, very like A. incisolobata, Eoem. (pi. 1. f. 3),
was found by myself, years ago, at Sholes Hook, near
Haverfordwest, in the Caradoc strata. It is in the
Museum of Practical Greology. The genus is new to
Britain.
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