LETTER OF TRANSMITTAL. 



U. S. Geological Survey, 



Division of Fossil Insects, 

 Cambridge, March 14, 1890. 



Sir: It is a source of great regret to me that tlie volume herewith trans- 

 mitted could not have been published during Dr. Hayden's life. It con- 

 tains the first fruits of an undertaking inspired by him and encouraged by 

 his aid. The extent of the task he intrusted to me more than a dozen years 

 ago has been, with the interference of other duties, the occasion of the 

 delay in its execution. The material has grown beyond all expectation, far 

 beyond anything that could liave been anticipated. 



As originally planned, when the Florissant beds were first carefully 

 exploited, the fossil insects other than those from Florissant were first to be 

 disposed of, and the latter were then to be taken up by orders. The plates 

 were accordingly executed (before the completion of the text) with that 

 plan in view, and the first ten plates herewith transmitted contain very 

 nearly all the extra-Florissant insects known ten years ago. Since then 

 their number has perhaps doubled. The succeeding plates contain the lower 

 orders of Florissant arthropods, ending with the Hemiptera. 



The text has been made to conform in large measure to the same plan, 



except that the insects of different localities and of different horizons have 



been arranged in one systematic series. Descriptions of a considerable 



number of species have been introduced for completeness' sake which are 



not figured, but of every one of these drawings have been finished and will 



be given in some future publication. The early portion of the text was 



written many years ago — the Arachnida and Termitina in 1881, most of 



the Odonata in 1882, the Ephemeridse and Planipennia in 1883, and the 



Trichoptera and Orthoptera in 1884; and, as the general remarks prefixed 



to each group were written on the completion of the study of that group, 



and would now have to be modified in some slight particulars, I have 



thought best to let these remarks remain as written, and to append at the 



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