642 THE LOWEK SILURIAN PERIOD. 



of the genera, and of the aid they afford in the determination of the 

 geological position of the St John group, leaving the descriptions and 

 figures of the species to be given in a future paper. 



" The fossils as yet known to occur in the rocks of the St John group, 

 are principally Trilobites, which are represented by quite a large 

 number of species, and Brachiopoda, which last are of more rare occui'- 

 rence. All these fossils ai-e preserved as casts or impressions, the 

 tests of the Crustacea and the shells of the Brachiopoda being usually 

 transformed into oxide of ii'on. 



"All the specimens have suffered more or less from distortion through 

 pressure and the metamorphosis to which the rocks enclosing them 

 have been subjected. The Trilobites occur also as detached fi-agments, 

 so that their accurate determination is not easy, and more material is 

 required in order satisfactorily to figure and describe all the species. 



" Representatives of four genera of Trilobites have been obtained thus 

 far from the St John rocks, viz. : — Paradoxides, Conocephalites 

 Agnostus, and a new genus (?) allied to Conocephalites. 



" The number of species in each genus has not yet been satisfactorily 

 made out ; but of Paradoxides there are at least five, of Conocephalites 

 seven, and of Agnostus and the new genus each one. 



" All the species appear to be new. One of the Paradoxides bears 

 a close resemblance to P. rugulosus, Corda, from the Etage C. of 

 Barrande, in Bohemia, and one of the Conocephalites is allied to C. 

 coronatus, Barrande, from the same fauna and horizon, though neither 

 is identical with the European species. 



" There are six species of Brachiopoda, belonging to the genera 

 Orthis, Discina^ Obolella, and Lingula. I have not been able to 

 identify any of the forms with described species. 



" Though all the species from the St John group are apparently new, 

 yet the occurrence of Paradoxides and Conocephalites, genera confined 

 entirely to the so-called Primordial fauna of Barrande, and every- 

 where characteristic of it, together with the strong likeness borne by 

 the St John species, in their fades, to those of the same genera of the 

 faunge of the "Primordial" in Europe and America, enable us unhesi- 

 tatingly to assign to the St John group, or at least to that lower part 

 of it which has afforded Trilobites, a geological position equivalent to 

 Barrande's Etage C. or to the Lower Potsdam of America. 



"Barrande uses the word fauna, in his term primordial fauna., 

 in a sense equivalent to epoch or horizon. A fauna is strictly a 

 collection of animals confined within a limited geographical area. 

 The terms "primordial fauna," "second fauna," are used with 

 propriety when applied to the groups of fossils characterizing the 



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