LETTER OF TRANSMITTAL. 



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rHiLADELi'HiA, 'February 18, 1887. 



Dear Sir : I have the honor to present to you for publication among 

 the Bulletins of the United States National Museum the manuscript of 

 a general work on the Batrachia of North America. It embraces the 

 results of a thorough study of the characters of the species, with their 

 variations, which has been rendered effective by the very full collection 

 contained in the National Museum, and which this work thus illustrates. 

 Besides this descriptive part, I have i»resented the results of a thorough 

 study of the osteology of the class, based on the material contained in 

 various museums of the United States and Euri)pe. I have expressed 

 these results largely in systematic form, in the belief that descriptive 

 zoiilogy will never be complete until the structure is exhausted in fur- 

 nishing definitions. Wherever practicable, reference is made to the 

 relations between the extinct and living forms. 



I have been greatly indebted to you for the use of the manuscript 

 l)re])ared by yourself and Dr. Girard many years ago with such a pub- 

 lication as the present one in view. Of the descriptions of the fifty- three 

 Urodela, nineteen are from your pen, and of the forty-seven Salientia, 

 twenty-t)ne are the work of yourself and Dr. Girard. This has materally 

 lightened my labor, the only additional work necessary to these descrip- 

 tions being such as increase of material has recpiired. In the same way 

 the figures of the external characters of the Urodela of which your de- 

 scriptions appear in the text, were prei)ared under your direction, and 

 the drawings of the crania of the same Urodela were partially prepared 

 at the same time, and have been completed by myself, now appearing 

 for the first time. The other drawings were made by myself, excepting 

 some which are credited to others at the proper places. 



Besides the collection of specimens in alcohol, the collection of skele- 

 tons prepared by yourself, and now part of the National Museum, has 

 been of the greatest service in the preparation of this work and of the 

 various papers by myself which have preceded it. 

 I am, with much respect, yours, truly, 



Prof. S. F. Baird, 



Secretary of the Sniithsonian Institution. 



E. D. Cope. 



