MILLIPED GENUS DIXIORIA — HOFFMAN 5 



So little is yet known of the comparative morphology of the cypho- 

 pods in most miUiped groups that little can be said of their value in 

 the differentiation of genera. It seems, at present, that the cyphopods 

 do not differ markedly from those of Brachoria and of the Trimaculata 

 group of Apheloria, although more detailed studies may reveal the 

 presence of very distinct features. 



Structm-al differences used in the separation of the forms of Dixioria 

 are of two kinds. Most conspicuous, and perhaps most fundamental, 

 are the differences in the shape of the male gonopods, and these are 

 the features customarily utilized by most students of the Diplopoda. 



During the course of my studies of polydesmoid milhpeds, however, 

 I have found that in most cases where the gonopods are singular 

 enough to indicate specific distinction, a close examination of the 

 material will reveal other correlated structural peculiarities. It is my 

 behef that, generally speaking, if a species is actually a valid one it 

 can be distinguished from its congeners by characters other than those 

 expressed by the male genitalia. 



In the present instance, Dixioria pela is separable from D. dactyl- 

 ifera by several tangible characters aside from the obviously disjunct 

 gonopods. These differences may be described verbally and are 

 mentioned both in the following key to species and in the diagnosis 

 of D. dactylifera. They are of interest in several respects. 



First, they serve to indicate that perfectly good taxonomic characters 

 may be disregarded in the general preoccupation with male genitalia 

 and color pattern — two variables which seem to have claimed the 

 attention of most American workers. Second, the discovery that 

 coxal spines may be present in one species and absent from another 

 suggests that theu- utilization in generic diagnosis may have to be 

 somewhat modified as our knowledge of variability of the character 

 improves. Heretofore, the presence or absence of coxal spines has 

 been considered to be constant in a genus. 



Despite the six or seven respects in which the two species of Dixioria 

 differ superficially, their general similarity in structure, color pattern, 

 size, and appearance is so great as to preclude any doubt of the 

 homogeneity^ of Dixioria as a generic entity. 



Taxonomic differences expressed by the gonopods of the male are, 

 to a considerable extent, qualitative and best appreciated by reference 

 to drawings. Nonetheless, it is quite possible to distinguish and 

 describe some of these differences verbally, and, with the development 

 of homologies and a terminology for the parts, to abolish the old 

 ambiguous phrase, "Gonopods as illustrated." In treating the gono- 

 pod characters in Dixioria, particular attention is here given to the 

 distal end of the telopodite, with its teeth and lobes, and to the shape 

 of the prefemoral process. 



