Page:Popular Science Monthly Volume 8.djvu/302

288 To take an example, or rather several examples together, for the force of the illustration will he thereby greatly increased.

Along the whole of the Atlantic, and the greater part of the Pacific coast of the United States, is found in great abundance, on sand-beaches, a species of tiger-beetle, Cicindela hirticollis, 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 similar 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 elevated 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 California, I think that we should infer that it is an unchanged survivor of the species which lived on the shores of the Cretaceous ocean, when the intercontinental gulf was still open, and a passage existed, moreover, toward the southwest, which connected with the Pacific.

The example I have given you of the geographical distribution of Cicindela hirticollis would be of small value, were it an isolated case; nor would I have thought it worthy of occupying your time, on an occasion like this, which is justly regarded as one for the communication of important truth. This insect, which I have selected as a type for illustrating the methods of investigation to which 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 large 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 received 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. hirticollis. I am disposed to believe, as no representative species occurs on the Pacific coast, and from its peculiar distribution, that it is older. Second, there is Dyschirius pallipennis, a small Carabide, remarkable among other species of the genus by the pale wing-covers, usually ornamented with a dark spot, This insect is abundant on the Atlantic coast, from New York to Virginia, unchanged in the interior parts of the Mississippi Valley, represented at Atlantic City, New Jersey, by a larger and quite distinct specific form, C. sellatus, and on the Pacific coast by two or three species of larger size and different shape, which in my less experienced youth I