THE ANCIENT EOCKS OF ST. DAVId's. '177 



Middle Arenig (continued). 

 Name. Localities. 



Tetragraptus crucialis, Salt Chiefly in the beds under the slate- 

 quarry, Whitesand Bay. 



Halli, Hopk. . Ditto. 



« Hicksii, Hopk Ditto. 



serra, Brong Ditto. 



Clemagraptus implicatus, Hopk Ditto. 



Dendrograptus arbuscula, Salt. MS. ... Ditto. 



• ilexuosus ?, Hall Ditto. 



Callograptus elegans, Hall : Ditto . 



Salteri, Hall Ditto. 



Dictyonema irregularis ?, Hall Ditto. 



Ufper Arenig. 



iEglina obtusicaudata, Hicks Llanvirn slate-quarry, near Aber-eiddy. 



Barrandea Homfrayi, Hicks Ditto. 



Calymene Hopkinsoni, Hicks Ditto. 



parvifrons, Salt., var. Murchisoni, 



Salt Porth-hayog, Ramsey Island. 



Illasnus Hughesii, Hicks Llanvirn quarry. 



Illgenopsis ? acuticaudata, Hicks Ditto. 



Placoparia cambriensis, Hicks Ditto. 



Phacops llanvirnensis, Hicks Ditto. 



Trinucleus Etheridgei, Hicks Porth-hayog, Ramsey Island. 



Ramsayi, Hicks Llanvirn slate-quarry. 



Beyrichia, sp Ditto. 



Dinobolus ? Hicksii , Davidson Ditto. 



Lingula attenuata, Sow Porth-hayog, Eamsey Island. 



Discina, sp Llanvirn slate-quarry. 



Orthis, sp Ditto. 



Ophileta, sp Ditto. 



Pleurotomaria llanvirnensis, Hicks ... Ditto. 



Bellerophon Uanvirnen sis, Hicks Ditto. 



Theca caereesiensis, Hicks Ditto. 



Conularia llanrianensis, Hicks Ditto. 



Orthoceras caereesiense, Hicks Ditto. 



Buthotrepis, sp Ditto. 



Didymograptus nanus, Lapw Porth-hayog, Ramsey Island. 



— — affinis, Nicholson Llanvirn quarry and Porth-hayog, 



Ramsey Island. 



— — bifidus, Hall Ditto, ditto. 



indentus, Hall Ditto, ditto. 



— - patulus, Hall Ditto, ditto. 



Nemagraptus capillaris, Emmons Llanvirn quarry. 



Dicellograptus moffatensis, ? Carr. Ditto. 



Climacograptus confertus, Lapw Porth-hayog. 



Diplograptus dentatus, Brongniart ... Ditto and Llanvirn quarry. 



Grlossograptus ciliatus, Emmons Llanvirn quarry. 



Llandeilo Geoup. 



The Llandeilo group, as it occurs in the neighbourhood of St. 

 David's and throughout Pembrokeshire, may be divided into three 

 subgroups on lithological and palseontological grounds. The Lower 

 Llandeilo consists of black slates interstratified with volcanic tuff, 

 and rests conformably on the Upper Arenig on the south coast of 

 Aber-eiddy Bay ; and the thick tuff-bed extending along that coast 

 shows the line of junction of the two groups. In Section Y. (fig. 6) the 



