EXPLANATION OF THE PLATES. 
PLATE I. 
FOSSILS OF THE CAMBRIAN ROCKS. 
[All the Figures on this Plate are original. ] 
HYDROZOA orn POLYZOA. (?) 
Fic. 1.—a, f. OLDHAMIA ANTIQUA, Forbes. 
O. antiqua.—Journal Geological Society of Dublin, vol. ii., p. 60, 1844; 
Ibid., vol. iv., p. 20, 1848 ; Transactions of the Royal Irish Academy, vol. 
xxili., 1858; Siluria, third edition, p. 28, Fossils, 2 ; Geological Maga- 
zine, vol. i., p. 385, 1865. 
a. A series of fan-like branchlets, in which the axis is barely perceptible. 
From a specimen collected by the Geological Survey of Ireland, in buff- 
coloured shales, Carrick Mountain, county of Wexford ; in the Museum, 
51, Stephen’s-green, Dublin. 
b. A single branchlet, in which the fasciculi, or branches, repeatedly divide 
and become more dense; var. O. disereta, Kinahan, from the same 
locality. 
c. A single branchlet, elongated, probably from the effects of cleavage ; 
same locality. 
d, An alternating series of branchlets, showing impression of axis in green 
grit, weathering brown with tracks and burrows of Arenicolites ; from 
rocks on shore at Bray Head; in the Museum, Geological Survey of 
Treland. 
e. An alternating series of a few branchlets, showing a kind of division into 
two branches, and a bead-like or nodular condition of the fasciculi. On 
the same slab are double burrow holes of Arenicolites didymus, Salter ; 
from green and red argillaceous slaty beds, rocks on shore at Bray Head, 
county of Wicklow; in the Museum, Geological Survey of Ireland. 
f. Rigid variety ; a series of fan-like branchlets in succession, and :mpressed 
upon each other, showing nodular character, from red and more argil- 
laceous beds, Kilruddery Demesne, Bray Head; Museum, Geological 
Survey of Ireland. 
B 
