340 COSTA RICAN EPIGOMPHUS (oDONATA) 



the posterior eye margin, a group of three, contiguous scars or 

 depressions (PI. XV, fig. 26, pgc) and in the corresponding posi- 

 tion behind the left eye two groups of two scars each. The dis- 

 tance beyond the right and left groups is very nearly equal to 

 the distance between the apices of the right and left superior 

 appendages of the male, when these are spread apart as in PI. 

 XV, fig. 24, pgc'. It seems highly probable, therefore, that when 

 pairing the apices of the superior appendages of the male were 

 applied against the hind surface of the female's head at the 

 positions now indicated by the scars, the scars being produced 

 by the tooth at the apex of each appendage. The fact that 

 there is more than one scar on each side of the female's head may 

 be readily accounted for by supposing that a permanent hold was 

 not immediately secured, and that some shght shifting of the 

 male's appendages occurred in the attempt, or that two or more 

 males may have paired with this female, as Dr. R. T. Hance 

 suggests. 



These post-genal scars, or cicatrices, as they may be termed, 

 lie in a wide and shallow groove which extends from its upper 

 end obhquely ventrad and mesad. This groove is bounded 

 superiorly by a transverse ridge whose summit is rounded off; 

 above this ridge are nine or ten sub vertical impressed lines (PI. 

 XV, figs. 25, 26, //) such as are found in corresponding positions 

 on the female of E. tumef actus (PI. XIV, fig. 22, II). Two possibil- 

 ities are suggested by the existence of these impressed lines: (1) 

 that they may serve as guides to direct the apices of the male's 

 superior appendages when he is attempting to grasp the female's 

 head, and hence must exist before pairing, or (2) that they are 

 produced by the tooth on the tip of those appendages when he 

 makes that attempt and that in consequence they also are cica- 

 tricial. Against this latter view is the circumstance that the 

 area over which they are found is much wider than the area 

 covered by the above-described post-genal cicatrices, whereas 

 one would expect approximately as many cicatrices as impressed 

 lines. It should be noted that the distribution of these impressed 

 lines is not exactly symmetrical on the two sides of the head. 



A slight linear depression (PI. XV, fig. 26, x) mesad to the lower 

 end of the most mesal of these impressed lines may possibly 



