REVISION OF BORARIA AND GYALOSTETHUS — HOFFMAN 329 



broader, and increasing in width back to about 14th segment; tergites 

 distinctly more convex than in the male; paranota smaller than in 

 male, the posterior corners produced only on segments 17-19. An- 

 tennae proportionately longer and more slender than in males, 6.0 mm. 

 in length. Legs widely separated, the intercrural distance at midbody 

 about 1.9 mm.; podosterna very low and with a deep, prominent 

 transverse groove separating anterior and posterior leg pairs. Inter- 

 zonal furrow distinct but shallow with a single row of punctations. 

 Spines of prefemora longer than in males, and slightly curved upward. 



Cyphopods of the form shown in figure 11; the recep table smaller 

 than in Boraria stricta and lacking macrosetae. 



Variation. — Boraria media differs from its two congeners in showing 

 considerable geographic variation in at least 2 characters. Aside 

 from the usual amount of individual and sexual variation in size and 

 proportions (summarized below), there is an appreciable difference in 

 body form which is related to geography, and two, largely vicarious, 

 variant forms in the gonopod structure. There is at present not 

 sufficient material at hand to permit a good analysis of these phenom- 

 ena, but some preliminary inferences can be drawn and commended 

 to the attention of some future worker. Unfortunately, few of the 

 female specimens are in satisfactory condition for accurate length 

 measurements, so that the following remarks have to be based largely 

 upon members of the male sex. 



As usual in this genus, females tend to be distinctly larger and 

 more robust than males. This is suggested by the following summary 

 of measurements (averages in parentheses) : 



sex number length (mm.) width (mm.) WjL ratio (%) 



males 10 24.0-33.0 (29.3) 4.9-6.7 (6.0) 19.1-22.9 (20.4) 



females 5 - 6.3-7.1 (6.8) 



Geographic variation in body proportions: On the basis of male 

 specimens only, it can be shown that variation in the body form can 

 be related in a general way to the species' horizontal distribution. 

 The narrowest specimen measured has a W/L ratio of 18.1%; the 

 broadest, 22.9%. Individual ratio figures, when plotted on a map, 

 tend to sort out with the highest percentages near the center of the 

 range, the lowest figures at peripheral points (fig. 12). Elsewhere in 

 the Xystodesmidae, there seems to be a tendency for broader body 

 form to be associated with more specialized genera and species, and 

 so perhaps we have here a case of centripetal widening of the body. 

 But the available data must be supplemented by far more evidence, 

 particularly from peripheral populations. 



Gonopod form: There are two distinct variants in gonopod form 



