on the Fossils of the older Deposits in the Rhenish Provinces. 305 



some parts of the north of Russia, while those of Eichwald, Pander, and Fischer 

 upon various parts of that vast empire, were also to be carefully considered. 

 Lastly, we could not omit the study of the valuable papers published on the older 

 deposits of North America, either in the United States by MM. Green, Conrad, 

 Troost, De Kay, &c., or in England by Dr. Bigsby and Mr. Stokes. If to this 

 already considerable mass of published documents be now added the observations 

 which one of us had collected in several parts of Europe, it will be seen that we 

 were partly in possession of the elements of a general work on the palaeontology of 

 the ancient formations. 



Once engaged in this course, we had only to complete our researches by a com- 

 parative examination of what had already been done, not only in Europe but also 

 in North America, where the deposits of this age are developed upon a scale of much 

 greater vastness ; and lastly, we were to add to all this such positive information as 

 is found in various scientific Transactions, or given by various travellers upon 

 other parts of the globe. After having eliminated the frequent repetitions in the 

 genera, and particularly of species, by comparison of the descriptions and figures 

 given by authors, as well as by that of the numerous specimens which one of us has 

 collected, we have obtained results from this first ge.neral sifting which we have 

 thought it might be useful to make known on this occasion, at least in a summary 

 manner. Surrounded by all these hitherto scattered and consequently ill appreci- 

 ated riches, we have thought it requisite to pause, and take a retrospective glance in 

 order to verify the course taken by science within ten years, and to expose rapidly 

 its progress and its present condition before continuing our march. 



We had therefore a twofold reason for placing this summary at the head of our 

 memoir, and making it form the first part. In the second we have described 

 the greater portion of those fossils of the ancient deposits of the right bank of the 

 Rhine which were still undescribed or imperfectly known, and to them we have 

 added some species from the Eifel. We have endeavoured to be simple, clear and 

 precise in our descriptions, but we have omitted nothing which was necessary 

 either to characterize the species or to distinguish them from their cognate species. 

 That which zoologically constitutes a species is not sufficiently defined to allow 

 us to limit our remarks to the enumeration of a few isolated characters ; it 

 is necessary to express all of them, because it is from the whole taken together 

 that the species results ; and this method is the more necessary for the fossils of 

 the ancient beds, because they are rarely found complete in all parts. If it be 

 observed that many authors have described and figured very incomplete organized 

 remains, of which they neither knew the dimensions nor all the characters, the 

 necessity of being more severe in labours of this sort will be felt, in order to avoid 

 encumbering the science with a multitude of names which really recal to the mind 

 nothing more than objects without form or interest. 



