BARRANDE ON THE TRILOBITE FAUNAS. 33 



For instance, the Orthocerata with large siphuncle, which are so 

 abundant in America, Russia, and Sweden, are altogether wanting in 

 Bohemia, France, England, and Ireland. On the other hand, the 

 majority of theTrilobite genera characteristic of this fauna, as lllcenus^ 

 Trimicleus, and others, are found in nearly all the above-mentioned 

 countries. The Trilobites, therefore, in this Period furnish the most 

 general and safe characteristics for the vertical and horizontal boun- 

 daries of the Group. In Bohemia we can subdivide the Group D, 

 which comprises this Second Fauna, into several well-characterized 

 series {d\, d2, d3, dA, d5), which, however, are still connected by a 

 large numerical proportion of common species. 



In England this fauna is recognized in the Llandeilo (=Bala) 

 group and the overlying Caradoc sandstone. In Sweden the Second 

 Fauna comprises, in vertical range, Angelin's two Regions C and D ; 

 it is the same fauna also that in the district of St. Petersburgh 

 extends from the blue clay to the limestone, inclusive. In France 

 the greater part of the Silurian series belongs to this same Period, 

 and I have identified several of the Trilobites with those of the Bo- 

 hemian Group D, as Acidaspis Buchi, Barr., and Dalmannia socialisy 

 Barr. In Portugal also this fauna is found in the Oporto district ; 

 and my friend De Verneuil has shown it to exist in Spain, from whence 

 he has brought specimens of Calymene Tristani, Brongn., Placoparia 

 Tourneminiy Ron., Illcenus Lusita?iicus, Sharpe, and others. 



In the United States this Second Fauna has very great superficial 

 extent. It alone has furnished all the fossils described by Hall in the 

 1st volume of the ' Palaeontology of New York.' All the Trilobites 

 figured in this work have their analogues in the Second Fauna of 

 European countries, with the exception of Triarthrus ; whilst, on the 

 other hand, several European types characteristic of this fauna are 

 still imknown in America. It would, without doubt, be very difficult 

 to persuade the geologists of the New World that they have not yet 

 discovered in their extensive region the representatives of the First 

 Fauna, before-mentioned. Time, however, will bring this about, to- 

 gether with the gradual but certain extension of these views. In 

 Bohemia, England, and Sweden we have the succession of the First 

 and Second Faunas well proved by the stratigraphical relations of the 

 beds that respectively comprise them. The actual proof of this 

 superposition in Europe leads to the conclusion that, if the First 

 Fauna exists in America, it must be found in the deposits beneath 

 those of the Second Fauna, and therefore must be sought for under 

 the Potsdam Sandstone, with which the Second Fauna commences. 



3. The Third Fauna, characterized by the Trilobites, commences 

 at the base of the Upper Silurian division. Almost all the genera of 

 the Trilobites that compose it pass up from the Second Fauna, but 

 are here represented by different and peculiar specific forms, having 

 special characters strikingly in contrast with those of the lower group. 

 Thus all the species of Illcenus of the Third Period are recognized by 

 their Bumastus-\\\ie appearance. All the Brontei have fifteen ribs on 

 the pygidium, whilst those two species belonging to the Second Fauna 

 {Br. laticauda, Wahl. sp., and Br. HibernicuSy Portl. sp.) have only 

 thirteen. The Cheiruri want the frontal margin, which those of the 



