REPORT OF THE SECRETARY. 27 



These districts are divided into a number of provinces of unequal size, 

 which are limited by differences in climate, and are therefore some- 

 times distinctly and sometimes vaguely defined. 



The mode of distribution of species in the Atlantic and Pacific 

 districts is entirely different. In the Atlantic districts a large number 

 of species are distributed over a great extent of country; many species 

 are of rare occurrence, and in passing over a distance of several hun- 

 dred miles but small variation will be found to exist. In the Pacific 

 district a small number of species are confined to a limited region of 

 country. Most species occur in considerable number, and in travel- 

 ling even one hundred miles it is found that the most abundant species 

 are replaced by others, but of a similar character. 



The object of the memoir is to give an account of what is known 

 of this class of insects in .Kansas, upper Texas, and Arizona, and to 

 furnish means for facilitating the further exploration of the whole 

 country in regard to the same animals. 



This will undoubtedly be considered a valuable addition to a branch 

 of zoology which, however insignificant it may appear to the popular 

 mind, is not only connected with questions of interest in relation to 

 abstract science, but also with the economical resources of the 

 country. 



The memoir, beside the colored map to which we have alluded, is 

 illustrated by tw T o engraved plates. 



The next paper consists of the result of magnetical and hypsomet- 

 rical observations in Mexico, to which is appended notes on the 

 volcano of Popocatepetl and its vicinity. 



In 1856 Baron Von Muller undertook an exploration of Mexico in 

 reference to its natural history, and proposed to the Smithsonian 

 Institution to make in its behalf a magnetic survey of the same country. 

 This offer having been accepted, an appropriation was made from the 

 Smithsonian fund to pay a portion of the salary of Mr. Sonntag, the 

 assistant of Baron Von Muller; and the magnetic instruments which 

 had been previously lent to Dr. Kane, and used by Mr. Sonntag 

 himself, as one of the assistants of that lamented explorer in his last 

 Arctic exploration, were furnished to the expedition for the contem- 

 plated survey. Several records of the unreduced observations made 

 at a number of places in Mexico, were at different times transmitted to 

 the Institution previous to the return of Baron Von Muller to Germany, 

 after which nothing more was obtained; and after considerable delay 



