MIDDLE CAMBRIAN. e. 
ele 
e2. Upper. 
Tremadoc Group. 
TREMADOC GROUP. 
N. Wales. S. Wales. 
Lower. Chiefly Black Slate. 
(Sedgwick, 1847). 
Sandstones, grey and bluish: iron beds: ferruginous slate, &e. 
el. Lower TreMADOC SLATE (Salter, 1857). A natural continuation of the Upper Lingula Flags. Chiefly 
black slate, but very ochreous in part. The fauna is essentially Middle Cambrian, but shews a tendency to include 
some few Lower Bala types, such as Niobe, Psilocephalus, &e. 
those of the Arenig Group, and those of the Upper are distinct from those of the Lower Tremadoc. 
tinguish the upper, e 2, from the lower group, e 1. 
The species however are all distinct, even from 
We dis- 


Case and | Reference to McCoy’s 
Column of 
ae | Synopsis : and Figures of Genera. 

G Trilobites. 
Gi | 
id a ale 
va are 

Gi 

Names and References; Observations, &c. 



| Niobe Homfrayi, Salter (Pal. Soc. Trans. Vol. 1. 
pl. 20, fig. 3). A genus intermediate in 
some sort between Asaphus and Ogygia. 
The labrum is round-pointed as in Ogygia, 
and the glabella lobed as in that genus, but 
broad as in Asaphus. The pleure bent, 
the axis of the body broad, the tail ample. 
Psilocephalus innotatus, Salter (id. pl. 20, figs. 
13, 14). A small Trilobite, allied to [dla@- 
nus, very abundant. 
Psilocephalus inflatus, Salter (Mem. Geol. Surv. 
Vol. 111. p. 316, woodcut 8). 
Conocoryphe depressa, Salter (Mem. Geol. Surv. 
Vol. ur. pl. 6, figs. 1—3). The species of 
this genus which occur in rocks above the 
Lingula flag, differ in not having the gla- 
bella lobes pronounced. 
Conocoryphe verisimilis, Salter (Mem. Geol. 
Surv. Vol. 111. pl. 6, fig. 13). 
Dikellocephalus (Centropleura) furca, Salter 
(Mem. Geol. Surv. Vol. 11. pl. 6, fig. 4, and 
pl. 8, fig. 10). The two blunt prongs to the 
hinder part of the tail distinguish this from 
D. celticus. It has also fewer ribs. 
Localities and Numbers. 


Tyn-y-llan, Tyn-y-dre, and 
other places near Trema- 
doe and Portmadoc. (Mr, 
Ash.) b. 329, 330, 362, 
(Mr. D. Homfray’s fine spe- 
cimens figured in the Pal. 
Tr.) from Penmorfa church. 
Tyn-y-llan, Tyn-y-dre, anc 
other places near Borth, 
Portmadoc. (Mr. Ash.) 
b. 352, 353, figured speci- 
mens. (Mr. D. Homfray.) 
b. 357, Penmorfa. (Mr. 
Homfray). Figured sp. 
Do. (Mr. Homfray). 
b. 354, Penmorfa village. 
(Mr. Homfray.) 
Llanerch, Moel-y-gest. 
| Garth, Portmadoc. (Mr. D. 
Homfray.) 
