Memoirs on the Coleoptera/Volume 1/New Species of the Staphylinid Tribe Myrmedoniini/Tribe Myrmidoniini/Group Athetæ
Tribe MYRMIDONIINI.
Group Athetæ.
The Athetæ constitute one of the largest and most intricate groups of the entire Coleoptera, and give rise to much diversity of opinion regarding scope and validity of genera. In my own opinion an intermediate course between the prevailing assumption of the present day, that such conspicuously different types as Atheta, Datomicra and Amischa, not to mention a score of more in addition, are not truly generic on the one hand, and the naming of so-called genera which differ among themselves only in sexual modifications at the ventral apex,—though often most important if supplemented by structural differences elsewhere,—on the other hand, is eminently proper. And, after all, what is to be gained by trying to aggregate these structural groups of species under a single name, as in the case of the comprehensive genus Atheta of the most recent school? Not only is there no discernible advantage in this procedure, but we subject ourselves to very great inconvenience in efforts to prevent duplication of specific names in such enormous single genera. This difficulty is also becoming pronounced in Stenus, but there it seems impossible to suggest the relief afforded by generic subdivision, which is so proper in Atheta because of the widely diversified facies as well as structure prevailing in the latter group; in Stenus the facies is very consistent throughout, and most of the subdivisions that have been proposed are apparently not true genera from any reasonable point of view. The European catalogue of Heyden, Reitter and Weise of 1895 is far superior to that of 1906, not only in its more sensible treatment of the Athetæ, as being composed of at least a few admittedly valid genera, but especially because our sense of propriety is not offended by the wholly unnecessary reversal of the usual succession of subfamilies, tribes and genera in the great family Staphylinidæ given in the latest edition of that work.
Another mistake frequently made, and a very serious one, is in assuming that nearly all exotic forms can be forced into the genera of purely European species. Some genera are common to Europe and America, but the isolation of the latter region since the middle Tertiary has sufficed for the evolution of many distinct types, so that at present there are a great many more endemic American genera than of those common to the two continents. The same remark applies as well to the species, the least resemblance between species of the two continents. The same remark applies as well to the species, the least resemblance between species of the two continents sufficing some superficial observers for a verdict of identity, which is false as a rule. There are some species common to America and Europe but not many, and they constitute an exceedingly small proportion of the whole number known; moreover virtually all such are likely to be cosmopolitan.
There have been but few attempts ever made to systematically arrange the genera and subgenera of Athetæ in accordance with their structural differences, and I would here bring forward one well known character to a position of primary importance in grouping the genera and subgenera; this relates to the degree of inflexion of the hypomera or inflexed sides of the pronotum, which divides the group into three very well defined sections thus:
| 1— | Hypomera moderately inflexed, nearly flat and wholly or in great part visible from the sides,—including such genera as Metaxya, Hydrosmecta, Atheta and many others. |
| 2— | Hypomera horizontal, though because of considerable warping of the surface, visible in very limited part from the sides,—including Dimetrota, Datomicra and others. |
| 3— | Hypomera strongly inflexed, in such manner as to be wholly invisible when viewed from the sides and including Acrotona, Colpodota, Coprothassa and others, as well as some related but distinct groups, such as the Hoplandriæ. |
The body in the first of these sections is more or less parallel and or larger size as a rule, in the second rather small to minute and generally with more tapering abdomen; in the third the body becomes on the whole still more limuliform, or with strongly tapering abdomen. The second character in point of importance relates to the formation of the sterna between the middle coxæ, and then follow several characters more particularly important in certain subsidiary sections, such as tarsal structure, impression of the abdominal tergites and form of the head, antennæ and lateral carinæ. Under the second of the above groups the have genera with the head parallel and others with the head basally inflated, and, among the latter, some with finely and others with coarsely faceted eyes. So it becomes sufficiently evident that we have among the Athetæ an unusual diversification of structural features.
The group Athetæ, as here construed, comprises the single genus Atheta of Fauvel, Bernhauer and some other recent authors.