ANNIVEESAEY ADDEESS OP THE PEESIDENT. 



89 



The Tremadoc rocks of Whitesand Bay also rest conformably 

 upon the Lingula-flags, and underlie the Arenigs, as at Eamsey 

 Island ; they strike north-east for 4 miles towards Abereiddy Bay. 

 The third exposure, at Tremanhire, shows the same stratigraphical 

 relations and succession, and has yielded fifteen out of the 30 

 new species described by Hicks as occurring at Eamsey Island. 

 This patch is now an isolated inlier surrounded by Lingula-flags and 

 Menevian beds, and with a large area of Longmynd rocks to the west. 

 The Pre-Cambrian ridge and Longmynd series now divide or sepa- 

 rate the two Tremadoc areas, which must have been once conti- 

 nuous. Dr. Hicks believes that the conditions under which these 

 rocks at St. David's were deposited were intermediate between those 

 of the shoal and shallow water in which the Lingula-flags were 

 deposited, and those of the deeper sea from which the finer muddy 

 deposits of the Arenig slates were thrown down, and that this was 

 probably one of the causes of the appearance in them of so varied a 

 group of organisms. 



There is some difficulty in comparing the Tremadoc rocks of 

 North with those of South Wales. At St. David's they are so inti- 

 mately connected with the underlying Lingula-flags and overlying 

 Arenig series that the boundary-line is almost arbitrary. Palaeon- 

 tologically they appear to be on the same horizon as the Lower 

 Tremadoc series of North Wales, the chief trilobite Niobe Homfrayi 

 with Linyulella Davisii and L. lepis connecting them. Yet the 

 mass of the faunas are entirely distinct, for out of the 42 North- 

 Wales and 30 South- Wales forms only the 3 above named are com- 

 mon to both. 



Thus out of the 4 North-Wales and 7 South- Wales Trilobita 

 only 1, Niobe Homfrayi, connects the two areas. Of the 4 

 genera and 9 species of Brachiopoda occurring in both areas only 

 2 species connect them, viz. Lingidella Davisii and L. lepis ; and 

 more remarkable still is the occurrence in Eamsey Island of the 

 earliest known Lamellibranchs in Britain, if not in Europe. The 

 Lower Tremadoc beds in that island have yielded 5 genera and 

 12 species, the first representatives known of that order ; 6 of 

 the same species occur inland at Tremanhire. Three of these genera 

 belong to the Arcidse, and one probably to the Anatinidse ; prior to 

 this discovery Medonia, Ribieria, and a species of Palcearca were the 

 oldest forms known, and were obtained from the Arenig beds at Lord's 

 Hill, Shelve. The last-named genus has been extracted from Lower 

 Silurian rocks in Spain, Bohemia, Prance, and Devonshire. These 

 bivalves are also associated with the earliest known Crinoid and 

 Starfish, Dendrocrinus cambrensis and Palceasterina ramseyensis. Still 

 more significant zoologically is the presence of a new genus with 

 four species of Trilobita, which Dr. Hicks has named Neseuretus. 

 This large and singular genus seems to have affinity with DiJce- 

 locephalus through its pygidium, with Calymene and Homalonotus 

 through the thoracic segments, and with the Conocephalidae 

 through the glabella. The four species and one variety are all 

 confined to the Lower Tremadoc rocks of Eamsey Island and 

 Tremanhire on the St.-David's promontory. None had occurred in 



