20 Proceedings. 
the head, body, and tail of nearly equal size—typical 
of the Ordovician or 2nd fauna; and this mingling of 
two faunas is a striking feature of the Tremadoc Slates. 
Of the first type we have :— 
(1) In N. Wales. Conocoryphe, Olenus, Angelina, ? Neseu- 
retus, Dikellocephalus. 
(2) At St. David's. Neseuretus, 5 spp., Dikellocephalus. 
(3) At Shineton. Conocoryphe (a Euloma), Olenus Salteri 
(Parabolinella Salteri), Olenus triarthrus, and Cono- 
phrys salopiensis. 
(4) At Carmarthen. Peltura punctata, Parabolinella sp., 
and Erinnys sp. 
Of the second type we have: 
(1) In N. Wales. Ogygia scutatrix, Asaphus affinis, Asa- 
phellus Homfrayi, Niobe Homfrayi, Psilocephalus 
2 spp., and Cheirurus. 
(2) At St. Davids. Niobe 2 spp., and Niobe Homfrayi. 
(3) At Shineton. Asaphus Croftii and Asaphellus Hom- 
frayi. 
(4) At Carmarthen. Ogygia marginata. 
Thus we see that the genera of the 1st and 2nd faunas in the 
Termadoc rocks are nearly equally represented. 
But besides these 7 genera of Trilobites belonging to the 
Qnd fauna, we have 2 genera of Graptolites, the earliest repre- 
sentatives of a family which attains such importance in the 
Arenig and succeeding formations. Here also the first Cepha- 
lopods (which hold such an important place in Scandinavia ati 
a rather later period) are found. 
These facts point clearly to the conclusion that the Termadoc 
Slates are Passage Beds from the Cambrian into the Ordovician. 
This view is confirmed also from the following evidence, that 
of the 33 genera and 89 species of the Tremadoc Slates, 
9 genera and 10 species have come up from the Lingula Flags 
(3 of these pass into the Arenig), and 11 genera and 18 species 
pass from the Tremadoc up to the Arenig. 
