There is one very prominent feature about the palaeontology of the ancient rocks of St. David's : this is the occurrence of four distinct species of the genus Paradoxides ; and this feature contrasts very strongly with the entire absence of the genus Olenus from these rocks.
On a comparison of the palaeontology of the St. David's rocks with those of the continent of Europe and of America, which seem to occupy nearly the same horizon, we have like features, to a very great extent, presenting themselves.
The lower fossiliferous horizon of Sweden, the Alum-shales, has been divided by Angelin into two groups. The lowest of these, " Regio B," contains forms of Paradoxides, among which we learn that Dr. Otto Torell has recognized two species that are St.-David's forms, viz. P. Davidis and P. Hicksii. The upper portion of the Alum-shales of Sweden, " Regio A" of Angelin, contains several forms of Oleni ; and from this portion of the series the genus Paradoxides seems to be absent.
The deposits upon which the Alum-shales of Sweden rest, the " Fucoidal Sandstones," contain within them purple beds ; and from these we have reason to believe that evidence of life has been obtained by Dr. Otto Torell in the form of an Obolella. In Sweden the genus Paradoxides is found accompanied by Conocoryphe (Conocephalites) ; and Trilobites of this genus are also found associated with Paradoxides in the St. David's promontory.
Regio B of Angelin is represented by the dark- coloured rocks of Porth-y-Rhaw ; and below these are strata which seem to be the equivalents of the Fucoidal Sandstones of Sweden, yielding an extensive series of fossils.
In N. Wales, on the E. and N.E. side of the Merionethshire anticlinal, Regio B is also represented, and is succeeded by the equivalents of Regio A, which, in the form of a thick series of dark-coloured sandstones and shales (Lingula-flags), contain several species of the genus Olenus.
In Bohemia, the primordial zone of Barrande, as shown by its fossil contents, is very near to the horizon of the Menevian group as exhibited in Wales. Trilobites appertaining to the genera Paradoxides, Conocoryphe, Ellipsocephalus, Sao, and Agnostus occur ; but no traces of the genus Olenus have been obtained from the Bohemian primordial rocks.
In Bavaria, Sir E. I. Murchison states that, in the neighbourhood of Hof, the primordial zone, " which consists of black siliceous slate, above 50 feet thick, contains Trilobites, which have been determined by Barrande to belong to Conocoryphe and Olenus ; " and in a letter from M. Barrande to Sir Roderick it is said that " with these primordial Trilobites are also associated two or three forms which everywhere characterize the second Silurian fauna (Llandeilo and Caradoc), i. e. Calymene and Cheirurus"*.
With reference to the fauna of the primordial zone of Hof, Barrande has remarked on the absence of the genus Paradoxides there-
- Quart. Journ. Geol. Soc. vol. xix. p. 362 ; Siluria, 4th edit. p. 374.
