Records of Distribution of Species of Isopods in Central and Southern United States, with Descriptions of Four New Species of Mancasellus and Asellus (Asellota, Asellidae)

In an effort to furnish data bearing on the problems of geographic distribution of the Isopoda, the following records are published. It seems highly desirable that more locality records be made available, since in this manner only may exact extent of distribution be ascertained. It should be pointed out that specific determinations of some forms in the genera Asellus and Mancasellus are attended with much difficulty. This is due to the fact that in most descriptions up to date stress has been laid on certain characters which are so broad that they are generic in value rather than specific, and conversely, on characters so variable that at most only local races may be defined by them, or only growth stages. As an example of the former, we cite the descriptions of mouth parts, and of the latter, number of segments in the antennae, and relative length of uropods. In a group in which the studies have been so scattered and uncorrelated, it is inevitable that there should be wide discrepancies of opinion as to what constitute characters of family, generic and specific rank, and value of various specific characters in separation of species. There are certain principles which should be considered carefully when describing species belongintg to the genera Asellus and Mancasellus. These are, first, determination of, and deletion of, generic characters and those of greater rank, second, specific characters should be used in such a manner as to utilize variational data rather than allow them to be confusing factors. In the specific descriptions in this paper certain customary "specific" characters have been intentionally omitted, such as proportions of the peduncular segments of the antennae. Such characters have been found to be more confusing than helpful, for variations of interspecific nature are slight, while growth variations are greater.