32 GEOLOGICAL MEMOIRS. 



These slates are analogous to the Olenus-slates of the Malverns, and 

 hoth rest on the azoic masses of the Harlech and Barmouth sand- 

 stone*. They are also altogether similar to the series (my Group C.) 

 to which since 1846 I have referred the Urfauna of Bohemia. The 

 fauna of Angelin's Regions A. and B.f (a slate and a limestone hed, 

 one resting on the other) consists of Olenus,Faradoxides,Conocephalus 

 (= Calymene,A^^Q\m), &c., and evidently corresponds to the Urfauna 

 of Bohemia and England. Lastly, the verbal communications with 

 which Professor Boeck of Christiania favoured me last summer, 

 enable me to recognize in Norway a fourth instance of this First Tri- 

 lobite Fauna, resting immediately on azoic rocks. 



It is very remarkable that in these four different countries this 

 First Fauna is altogether distinct from the next succeeding fauna, not 

 a single species being common to the two. The other organisms 

 that accompany the Trilobites of the Urfauna are rare, and, on the 

 whole, little characteristic, as they differ in the different countries. 

 Thus I have in Bohemia OrthisRomingeri and three Cystidece, amongst 

 which is Lichenoides priscus. In England there are the Lingula 

 Bavisii of the Lingula-flags of Wales, — a doubtful form allied to 

 Eurypterus, — and some indistinct remains of Graptolites, which I 

 have seen in the Museum of the Geological Survey in London |. 

 What forms accompanied the Trilobites in the Urfauna of Sweden, 

 I do not yet know. In any case, it is probable that, as in Norway 

 and the other two countries, but few fossils occur, as there has been 

 no notice of them as yet. 



Thus, in each of the four regions here spoken of, Trilobites seem 

 almost alone to have constituted the Fauna of the First Period ; and 

 this character of the Urfauna is the more worthy of notice, as it forms 

 a striking contrast to the manifold composition of the next succeeding 

 fauna. 



2. The Second Fauna is that of my Group D. This also possesses 

 peculiar genera, asAsaphus (=Isotelus, SympJiysurus,HemicrypturuSj 

 Niohe, Megalaspis, &c.), Trinucleus, Ogygia, Remo^oleurides, Placo- 

 paria^ Zethus, Amphion, j^glina, Dionide, &c. ; besides others, 

 whose maximum development is here attained, as Illcenus and Ampyx^ 

 and some, viz. Harpes, Bronteus, Cheirurus, Phacops, &c., which 

 have their greatest development only in the Third Fauna. In general 

 the genera more or less peculiar to this Second Fauna (Asaphus, 

 Ogygia, AEglina, Dionide, Illcenus, and even some species of Tri- 

 nucleus), have a very reduced thorax, with a large pygidium,— 

 strongly contrasting with what we have seen in the First Fauna. It 

 is also to be remarked that the genera here reach their numerical 

 maximum, although that of the species is not attained until much 

 later. The Second Fauna is connected with the Third by a small 

 number only of common species. 



The several classes of Molluscs, Cephalopoda, Brachiopoda, Ace- 

 phala, Pteropoda, &c., have already numerous representatives at this 

 Period, which, however, have a veiy unequal geographical distribution. 



* See also Bulletin Soc. Geol. France, 2 ser. ]851, p. 268 et seq. 



f Palseontologia Suecica, Lief. 1. :|: \_Vide supra, p. 31, note.] 



