110 BRITISH PALASOZOIC SPONGES. 
belonged to the same Sponge. In some instances, however, the spicular ropes and 
detached spicules occur in beds in which no hexactinellid spicules have as yet been 
met with ; but this may in part be accounted for by the fact that even during the 
life of the Sponge the anchoring spicules would be buried in the bottom ooze, and 
would thus escape the disturbing influences which have probably scattered and 
destroyed the body-spicules after the death of the Sponge. 
These anchoring spicules, in the best preserved examples, exhibit all the 
characters of similar spicules in recent hexactinellid Sponges met with in deep-sea 
dredgings. They are composed of silica deposited in concentric layers, they are 
traversed by an axial canal, and many of them likewise terminate in four recurved 
hooks. Further, in one species the surface of many of these spicules is ornamented 
with slight projecting frills of a character similar to those present in the anchoring 
spicules of the recent Hyalonema mirabile, Gray. As the recent anchoring spicules 
are in all cases associated with a Sponge body consisting of hexactinellid spicules, it 
may be concluded that the fossil anchoring spicules were similarly associated, even 
though they now occur in beds in which the hexactinellid body-spicules are rare or 
apparently absent. 
Pyritonema, M‘Coy, and Acestra, F. Roemer, have been founded exclusively on 
the bundles of anchoring spicules. Onthe ground of priority, M‘Coy’s term might 
be claimed as the designation of this genus, but as objection could be taken to 
employing it for hexactinellid body-spicules as well as for the anchoring spicules, 
it seems preferable to adopt Zittel’s name Hyalostelia, which includes both kinds of 
spicules. 
Both M‘Coy and Portlock regarded the anchoring spicules occurring in the 
Carboniferous Limestone of Ireland as the tubes of annelids, and placed them 
in the genus Serpula. 
Hyalostelia is first known in Cambrian strata (Tremadoe Group), and it is also 
present in Ordovician, Silurian, and Lower-Carboniferous Rocks. Detached 
hexactinellid spicules in the Upper Chalk have been assigned to the genus, but the 
ropes or bands of anchoring spicules have not been met with above the Carboni- 
ferous Rocks. 
3. Hyatostenra rasciounus, M‘Coy sp. Plate I, figs. 3, 3 a, 3 0b. 
1850. Pyrrronema Fascrcutus, M‘Coy. Ann. and Mag. Nat. Hist., ser. ii, 
vol. vi, p. 273. 
1854. — -- Morris. Cat. Brit. Foss., p. 63. 
1855. = — M‘Coy. Brit. Pal. Foss., p. 10, pl. i8, fig. 13. 
1869. Hornyron expranatum, Hicks. Geol. Mag., vol. vi, p. 534, pl. xx, 
figs. 1 a—e. 
