EXPLANATION OF THE PLATES. 9 
Uprer Lincuta Fracs.—Penmorfa Church, and Carreg-wen farm, near 
Portmadoc, North Wales; also in the shales of White-leaved Oak, &c., Mal- 
vern. In certain beds of the Lower Lingula Slates, which are full of iron, 
and contain some volcanic ash, the Agnostus princeps occur in millions. 
Ib., p. 248. Tremapoc SLATE.—Portmadoc. Lowrr LLANDEILO.—St. 
David’s Head, Pembrokeshire ? 
Other localities mentioned in list of Lower Lingula Flag fossils: Maentwrog 
Waterfall, and other places near Ffestiniog. Jb., p. 247. 
Fig 3.—a, b, ParapoxipEs Davinpis, Salter. 
Journ. Geol. Soc., vol. xix., p. 275; and xx., pl. xiil., figs.1-3. Decade 
Geol. Survey, No. 11., pl. x., figs. 1-8. 
a. Reduced to half natural size from Journ. Geol. Soc., vol. xx., pl. xiii., 
fig. 1. The number of body rings is not complete. 
b. The tail, reduced to the same proportions; from fig. 2 on the same plate 
(the restored parts are drawn in outline). 
The discovery of this large and well-developed Trilobite as_a British fossil 
by Mr. Salter in strata so low in the series as the Lowest Lingula Flags is 
of the greatest interest, especially as the range of the genus, so extensive 
abroad, had been until lately limited in this country to a single specimen 
only, it being only a few years since it was found in any considerable num- 
bers, ata single locality in South Wales, as weare informed by Mr. Salter, 
in Decade 11, p. 2; that paleontologist observing that some of the frag- 
ments collected indicate a fossil of 16 or 18 inches in length. The broad 
club-shaped glabella (central portion of head), long spines proceeding from 
each side of the head, and numerous (17 to 20) body rings, readily distinguish 
this group, which includes the largest known Trilobites, from all others, and 
yet is the earliest type, or nearly so, of the whole Trilobite family. Ag- 
nostus accompanies it in all countries where it has been observed. De- 
cade 11, Text to pl. x., p. 2. 
Lowest Lineuta Fracs.—Port Rhraw and Solva Harbour, both near St. 
David’s Head, South Wales; also north of Dolgelly, North Wales. De- 
cade 11, Text to pl. x., p. 4: M.G.S., vol. ii., p. 247. 
Fic. 4.—OLenus micrurus, Salter. 
Mem. Geol. Survey, Dec. 2,pl.9; Siluria, 3rd Edition, p. 45; Foss. 4, 
fiz. 2; Mem. Geol. Survey, vol. iii. p. 300, pl. 2, fig. 5, 6, repeated from 
Dec. 2, pl. 9, fig. 1, 3. 
From the original figure in Decade 2, pl. 9, fig. 1. This Trilobite is the first 
described British example of the genus Olenus, and is more familiar to us 
from its figures than the following species, O. cataractes, although, as Mr. 
Salter observes, it is by no means a common fossil, as the latter appears to 
be the ordinary form in the lower black shales of North Wales. Decade 11, 
Text to plate 8. Olenus and Paradoxides in Britain, as well as on the 
Continent, are among the most ancient genera of Trilobites in the lowest 
Silurian rocks. 
Lower Lincuta Fracs.—Trawsfynydd ; Cwm-y-Swm, gold mine ; Dolgelly, 
Merionethshire ; Marchllyn-mawr, near Llanberis, Caernarvonshire ; 
Treflys ; Borth, Portmadoc; Premadoc, &e., North Wales. 
Cc 
