REVISION OF BORARIA AND GYALOSTETHUS — HOFFMAN 309 



All of the localities mentioned may be located in the "Rand-McNally 

 Commercial Atlas of the United States." 



Taxonomic Characters 



As in preceeding papers in this series, I wish to preface the taxonomic 

 treatment with a consideration of various structural characters that 

 have been found useful in the separation of genera and species or in 

 the recognition of similarities between such taxa. The following 

 account may appear somewhat extended, but this is due to the fact 

 that it contains both the description and evaluation of the characters 

 involved; also, it is due to the fact that, in some cases, I can now 

 attempt the classification of certain features, such as the sterna as 

 they occur in the Xystodesmidae at large and not just as they occur 

 in the genera discussed in this paper. 



It is patently impossible to utilize, for practical taxonomic pur- 

 poses, all of the points of similarity and difference that can be recog- 

 nized in groups of related species. I think, however, that in diplopod 

 systematics we should go beyond mere "key characters" — at least in 

 formal descriptions or definitions of species. The present considera- 

 tion of sexual dimorphism is a case in point, for even though series 

 of both males and females may be needed to establish the extent of 

 size or proportion of dimorphism, the phenomenon itself is certainly 

 a valid part of the makeup of many species and, therefore, should be 

 taken into account. We need not rely upon the stronger dimorphism 

 of Boraria deturkiana to separate that species from B. media, but it 

 is nonetheless a point of difference and one which is useful in deter- 

 mining comparative levels of divergence in this genus. The same 

 point might be made for differences in life history, habitat preferences, 

 and so on, when this information becomes available. 



Body form. — The relative proportions of the body offer useful 

 comparative data on relationships of species even though they may 

 not be of immediate value in identifying individual specimens. One 

 factor which influences the mensural proportions is the degree of 

 development of the paranota: specimens with well-developed paranota 

 naturally appear much broader in relation to the body length, and 

 this is reflected in the ratio of width divided by length (referred to 

 hereinafter as the W/L ratio). Normally males tend to have a 

 higher ratio since the paranota are larger in comparison to the diam- 

 eter of the segmental body cavity. This is not always true, however, 

 and among the species here considered, the ratio tends to be about 1% 

 greater in females. The ratio is not obtainable with a high degree 

 of accuracy since the length of preserved specimens is difficult to de- 

 termine, but with a little practice one can at least secm*e uniform 



