AMERICAN ODONATA. 205 



THE SUBGEN(J!§i STYL.IIRIIS IVEEDHAIVI: SEL.YS' 

 GROUPS VI AXD VII OF THE GEIVUS G09I- 

 PHUS (ODONATA), AXD ON THE POST- 

 ANAL €ELL,S IN THE EATTER. 



BY E. B. WILLIAMSON. 



Size medium or large ; thorax normally dark Avith paler mark- 

 ings ; a pale stripe between the mid-dorsal carina and the humeral 

 suture, isolated, no.t continuous above or below with other pale 

 areas; in adults the general color of thorax and abdomen is a very 

 dark reddish brown or black (excepting in plagiakis, where 'the 

 thorax is somewhat lighter and the abdomen is brown), while the 

 pale thoracic markings are bluish green in color (in tenerals yellow 

 or greenish yellow). Front wings with two posttriangular cells (in 

 sciidderi usually, and in other species frequently, three in the first 

 row) ; the branches of the anal vein normally enclosing first two 

 open cells followed by two rows; the first postanal cell* irregular 

 in form, its length about one and one half times its maximum width, 

 one side formed by the second branch of the anal vein, which 

 branch is distinctly angulated where it is met by the vein separating 

 the first and second postanal cells ; portion of Snal vein bounding 

 the first postanal cell longer than the portion of the second branch 

 of the anal vein bounding the same cell ; pterostigina ordinary or 

 long. 



S . — First hamule slender, simple, partly or entirely concealed by 

 the second, not unguiculated ; second hamule laminate, as seen in 

 profile tapering to an acute apex ; sheath of penis large, rounded. 

 Superior abdominal appendages widely divaricate, seen in profile 

 the upper edge not as convex as in related species (frateruus, cras- 

 ■sus and the dilatatus group), beyond the middle the outer side 

 bevelled away to the apex, the bevelled portion with a narrow 

 externo-ventral shelf with a crenulate mai-gin ; inferior appendage 

 with its branches about equally or slightly more divergent than the 

 superiors. 



® The cells enclosed between ttiese two branches of the anal vein may be called 

 the postanal cells, thus avoiding any confusion with the anal triaiigle of authors ; 

 they make up the middle one of the three postcostal areas. 



TRANS. \M. ENT. SOC, XXVII. MAY, 1901 



