PREFACE. XXVII 



Viviparous Quadrupeds of North. America," was prepared, the materials at their command were 

 far less extensive than have been at mine, and that many species which they could only examine 

 in the museum of London, Paris, Berlin, and Ley den, are now to be found in the Smithsonian 

 collection in a profusion of specimens of the most satisfactory and perfect character. 



An apology is necessary for the delay which has taken place in the completion of the general 

 reports on the zoology of the Pacific Eailroad surveying parties. This has arisen from the fact 

 that, from the first organization of these expeditions, in the spring of 1853, nearly to the present 

 time, one or more has been in the field, and engaged in fresh examinations ; so that until all 

 the specimens expected were received, the general systematic account of zoological results could 

 not conveniently be prepared. The examination of the materials was actually commenced early 

 in 1855, and many of the articles written in that year and in 1856. With the continuous 

 accession of additional specimens, it became finally necessary to re-write, alter, or extend all 

 that had been prepared prior to the present year (1857.) It is to this that the frequent want 

 of uniformity is due, the time allowed not being sufficient in many cases to permit the re-working 

 of the whole matter. The measurements of the specimens were at first made in inches and 

 lines, but that of hundredths was finally adopted ; it is to this fact that the presence of the two 

 different divisions of the inch is attributable, it not being convenient or possible to make the 

 measurements conform throughout, as would have been desirable. 



It is, perhaps, unnecessary to state that the matter of the present report is entirely original 

 throughout, the few cases in which extracts from other authors are made being so indicated. 

 With very few exceptions, all the references in the synonymy have also been personally made 

 and verified. Where this was not possible, the synonym is enclosed between quotation marks. 



In explanation of the too frequent occurrence of typographical errata in the body of this 

 report, it is proper to state that, owing to various circumstances, the work was necessarily passed 

 through the press with a rapidity probably unexampled in the history of natural history 

 printing, allowing very little opportunity for that critical and leisurely examination so neces 

 sary in correcting a work of the kind. For most of the time the proof has been furnished and 

 read at the rate of twenty-four to thirty-two pages per day ; nearly 400 pages having been set 

 up, read, and printed during the first half of July alone. The same cause has also interfered 

 with the preservation of perfect uniformity of arrangement and detail throughout. In some 

 cases, accidents to the form while on the press have caused the loss or transposition of letters, 

 words, or paragraphs ; as, among others, the exchange of characters of Orders VIII and IX, 

 on page 1, referred also to on page 625. For excuse of errors in the use of technical terms, in 

 the formation and inflection of scientific names, and for all other shortcomings, the writer can 

 only throw himself upon the kind indulgence of his readers, partly in consideration of the fact 

 that, owing to the urgent necessity for a speedy completion of the volume, no time was allowed 

 for any revision of the manuscript as a complete work, nor, indeed, of its separate portions, 

 and that for much of the time the preparation of the manuscript was only a few hours in 

 advance of its delivery to the compositor. 



A few words in explanation of the plan adopted in preparing the articles of the present 

 report may not be out of place. I have usually made the entire detailed description of the 

 species from one particular specimen, (often indicating it by number,) mentioning afterwards 

 the variations presented from this type by the others before me. The specific diagnoses alone 

 contain a combination or selection from the characters of several specimens. 



The numbers attached to the specimens, as enumerated, are those which they bear in the 



