118 BRITISH PALASOZOIC SPONGES. 
spicules cannot be recognised. Longitudinal and transverse sections, however, 
clearly show its affinities with the genus, and so far as can be ascertained from the 
condition of the specimen it belongs to the present species. 
Distribution —Ordovician : Girvan, Ayrshire (Prof. H. A. Nicholson) ; Trenton 
limestones, near Chicago (Dr. W. R. Head). Silurian: Wiinge, Isle of Gothland 
(Prof. G. Lindstrém); St. Petersburg, Russia; Perry County, Tennessee (F. 
Roemer) ; Lower Helderberg Group, Dalhousie, New Brunswick; Scoharie, New 
York. Glacial drift: Sadewitz, Lower Silesia (F. Roemer); Lyck, East Prussia ; 
Rombitten, West Prussia (F. Roemer) ; Island of Sylt, Holstein (Haas). 
6. Hyatostenia Smrram, Young and Young sp. Plate I, figs. 4, 4a. 
1877. Hyautonrma Smuirnit, Young and Young (in part). Ann. and Mag. Nat. 
Hist., vol. xx, p. 426, pl. xiv, 
figs. _—8, 5—12, 14—17. 
1880. — ? GirvanensE, Nicholson and Etheridge, junr. Mon. Silur. Foss. 
Girvan, Fase. ii, p. 239, pl. xix, 
figs. 1—1 8. 
The references to this species and its characters will be more fully given in 
treating of the Carboniferous Sponges; it is introduced here to include a specimen 
of elongated spicular rods from Ordovician strata. 
The spicular rods in the only specimen known from this horizon are not united 
in bundles, but they are detached and distributed irregularly at short distances 
from each other in the rocky matrix. They are circular in transverse section, 
with apparently smooth surfaces. Their length and natural terminations are 
unknown. They vary very considerably in thickness, the slender rods not 
exceeding *15 mm. in diameter, whilst the stoutest spicules are 1-4 mm. The axial 
canals are occasionally preserved. 
These spicules were referred by Messrs. Nicholson and Etheridge to a distinct 
species, principally on account of peculiar transverse bands of varying thickness, 
which occur at intervals in the spicules and were believed to indicate a distinct 
structural feature. In sections of the type specimen from which the figures on 
Plate I are drawn, the spicules exhibit, by polarized light, the optical characters of 
chalcedonic and crystalline silica, but in the banded intervals the silica has evidently 
been replaced by some other mineral. The replacement has been effected along 
minute transverse fissures in the spicules, and the same mineral has likewise been 
deposited in places on their outer surfaces. It seems clear, therefore, that the 
bands are not original, but merely secondary structures resulting from fossilization. 
In their relative proportions these spicular rods agree with those forming the 
