EXPLANATION OF THE PLATES, 11 
PLATE V. 
FOSSILS OF THE LOWER LLANDEILO OR TREMADOC 
SLATES. 
CRUSTACEA.—TRIL OBITA. 
Fria. 1.—CoNnocorYPHE DEPRESSA, Salter. 
Memoirs Geological Survey, vol. iii., p. 307, pl. vi. fig. 1. Ellipsoce- 
phalus 2? depressus, Siluria, third edition, p. 47, Foss. 7, fig.2. The head 
of this Trilobite is remarkably broad ; the eyejis small: the azis, or cen- 
tral portion of the body, is wide, and the whole animal much depressed or 
flattened. 
Position and Locality. Lowrr TremMapoc. Wern, Penmorfa; and above 
Penmorfa Church. 
Fic. 2.—a, b. ANGELINA SEDGWICKII, Salter. 
Geol. Surv. Decade 11, pl. vii., fig. 1-5. A. Sedgwickit, Siluria, third edi- 
tion, 1859; p. 53. Foss. 9, fig. 2. A. subarmatus, Ibid. fig. 3, specimens 
distorted by cleavage. 
a. From the original figure in Decade 11, pl. vii., fig. 2. 
b. Original.—From a specimen in the collection of the Geological Survey of 
Ireland. Locality, Garth, opposite Portmadoe, in grey slate. 
This Trilobite is distinguished by its long head spines; the glabella is 
smooth, and without lobes; the body segments are provided with an an- 
gular fulcrum, so constructed as to enable it to roll up. The tail is small, 
and sometimes bordered with spines. 
Both figures show distortion in different directions, the effects of mechani- 
eal action, or what is termed cleavage, upon the rock in which these fossils 
are imbedded, and are introduced to show the caution and amount ofjudg- 
ment necessary in the determination of fossils affected in a similar manner, 
where there is so great a departure from the original form. 
Upper Bens oF THE TREMADOC SLATES.—Garth Hill, east side of the Traeth 
Bach, Tremadoc ; Portmadoc quarries ; Tuhwnt-yr-bwlch; Under Garth, 
&e.; Dendraeth; Ynys-Tywyn. Mem. Geol. Surv., vol. ili., pp. 253, 
310. 
Fig. 3.—ASAPHUS AFFINIS, J‘ Coy, sp. 
Tsotelus affinis, M‘Coy, Synopsis, Brit. Pal. Foss., pl. i. F, fig. 3. A. 
affinis, Memoirs Geological Survey, vol. iii, p. 310, pl. viil., fig. 15, 
