INTRODUCTORY REMARKS. 



This being a strictly palseontological report, any extended remarks on 

 tlie geological formations from wliicli the fossils described were obtained 

 are not expected, and would be out of place here. A few words, however, 

 respecting some points on which the specimens investigated throw more or 

 less light, seem to be necessary to a clear understanding of the palaeontology 

 itself. 



Before proceeding further, however, it is proper to state here, that, in 

 order to give as full and complete an account of the palaeontology as possible 

 of the district explored, some collections brought from the same region more 

 than ten years since, by Col. J. H. Simpson, of the United States Topograph- 

 ical Engineers, while conducting a Government expedition through the same 

 country, have also been included. In 1860, the writer published, in the Pro- 

 ceedings of the Philadelphia Academy of Natural Sciences, brief preliminary 

 descriptions of the new species of fossils contained in Colonel Simpson's 

 collection, and soon after prepared, for that gentleman's report, more 

 extended descriptions and figures of the same. Unfortunately, however, 

 Congress failed to make the necessary appropriation to publish Colonel 

 Simpson's report. Consequently, the large amount of important information 

 contained in the same remains unpublished; and, as it is now extremely 

 improbable that his report will ever be printed,* at any rate with the 

 accompanying illustrations, it has been thought desirable that we should give 

 here descriptions and figures of the new fossils of his collection, now in the 



* Since this was written and revised, Colonel Simpson's report has been pub- 

 lished. 



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