288 THE POPULAR SCIUNCE MONTHLY. 



To take an example, or rather several examples together, for the 

 force of the illustration will he therehy greatly increased. 



Along the whole of the Atlantic, and the greater part of the Pa- 

 cific coast of the United States, is found in great abundance, on sand- 

 beaches, a species of tiger-beetle, Cicindela liirticolUs, an active, 

 winged, and highly-predaceous insect ; the same species occurs on the 

 sand-beaches of the Great Lakes, and, were it confined to these and 

 simihir localities, we would be justified in considering it as living there 

 in consequence solely of the resemblance in the conditions of existence. 

 But, it is also found, though in much less abundance, in the now ele- 

 vated region midway between the Mississippi and Rocky Mountains. 

 Now, this is the part of the continent which, after the division of the 

 great intercontinental gulf in Cretaceous times, finally emerged from 

 the bed of the sea, and was in the early and middle Tertiary converted 

 into a series of immense fresh-water lakes. As this insect does not 

 occur in the territory extending from the Atlantic to beyond the 

 western boundary of Missouri, nor in the interior of Oregon and Cali- 

 fornia, I think that we should infer that it is an unchanged surviA'or 

 of the species which lived on the shores of the Cretaceous ocean, when 

 the intercontinental gulf was still oj^en, and a passage existed, more- 

 over, toward the southwest, which connected with the Pacific. 



The example I have given yoii of the geographical distribution of 

 Cicindela hirticolUs would be of small value, were it an isolated case ; 

 nor would I have tiiought it worthy of occupying your time, on an 

 occasion like tliis, which is justly regarded as one for the communica- 

 tion of important truth. This insect, which I have selected as a type 

 for illustrating the methods of investigation to whicli I invite your 

 attention, is, however, accompanied more or less closely by other 

 Coleoptera, which like itself are not particular as to the nature of their 

 food, so long as it be other living insects, and apparently are equally 

 indifferent to the presence of hxrge bodies of salt-water. First, there 

 is Cicindela lepida, first collected by my father, near Trenton, New- 

 Jersey, afterward found on Coney Island, near New York, and re- 

 ceived by me from Kansas and Wisconsin ; not, however, found west 

 of the Rocky Mountains. This species, thus occurring in isolated and 

 distant localities, is probably in process of extinction, and may or may 

 not be older than C. hirticolUs. I am disposed to believe, as no i-ep- 

 resentative species occurs on the Pacific coast, and from its peculiar 

 distribution, that it is older. Second, there is Dyschirius pallij^ennis, 

 a small Carabide, remarkable among other species of the genus by the 

 pale wing-covers, usually ornamented with a dark spot, Tiiis insect 

 is abundant on the Atlantic coast, from New York to Virginia, un- 

 changed in the interior parts of the Mississippi Valley, represented at 

 Atlantic City, New Jersey, by a larger and quite distinct specific 

 fornij C. sellatus, and on the Pacific coast by two or three species of 

 larger size and different shape, whicli in my less experienced youth I 



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