ART. 10. DRAGOISTFLIES OF GENUS ACIAGRION LAIDLAW. 3 



tigma of the forewing larger than that of the hind wing, whilst the 

 anal appendages of the males of some of the species at least {A. 

 tillyardi, A. olympicum) bear a strong resemblance to the coiTe- 

 sponding structure of some of the African species, Afncallagnna 

 glaucum (Burmeister)^ for example. 



On the whole we may conclude that the genus is a specialized end- 

 branch of the great Enallagma series. 



In the following table I have attempted to give the differential 

 characters of all the species (six in number) which I have been able 

 to identify in the material available to me. To make the table as 

 complete as possible I have added a note on species I have not seen, 

 derived from the descriptions given by the author in each case. 



In this table the expressions " moderate size," "rather large " must 

 be taken as relative only. 



o.^ With blue coloring on abdomen, the blue being especially vivid on the 

 first three and on the last three segments. Head and syntliorax also 

 with blue markings, the latter with blue antehumeral stripes, and with 

 the sides blue. 



6.^ Species of moderate size (abdomen of male 24-26 mm., of female 24 

 mm.; hind wing of male 15-16 mm., of female 16-17 mm.). In 

 the male, segments 8, 9, 10 of abdomen entirely blue (or in speci- 

 mens from some localities segment 8 has small, paired, black basal 

 markings on the dorsum). Female similar, but blue less vivid, 

 and segment 8 has a longitudinal, black band on the dorsum not 

 reaching the apex of the segment, whilst 9 has small, paired, 

 basal spots. Postiiodal nerves on forewing 10-11. 



A. hisopa de Selys. 

 6.^ Species of moderate size (abdomen of male 24..5 mm., of female 22..5 

 mm.; hind wing of male 17.5 mm., of female 17.5 mm.). Rather 

 robust for its size when compared with other species of the genus. 

 In both sexes the last three segments of the abdomen are defi- 

 nitely dilated. In the male, segments 8 and 9 of abdomen bright 

 blue, dorsum of segment 10 black. The female has a dorsal, 

 black band on segments 8 and 9, not quite reaching the apex of 9, 

 whilst 10 is apparently blue, unmarked with black. Postnodal 



nerves on forewing 12 A. tillyardi Laidlaw. 



&.' Small species (abdomen of male 22-24 mm., of female 23 mm.; hind 

 wing of male 15 mm., of female 15.5 mm). Very slendei-. In the 

 male, segments 8, 9, 10 rich blue, 8 with a black, dorsal triangle, 

 its apex anterior but not usually reaching the base of the seg- 

 ment, 9 entirely blue, 10 has a black X-shaped mark on the dor- 

 sum. Female with a broad dor.sal band of uniform width on 8, 

 segment 9 with a broad basal triangular mark of black, 10 en- 

 tirely blue. Postnodal nerves on forewing 9. 



A. occidentale Laidlaw. 



3 1 have used Kennedy's generic names here. It seems to me convenient to distinguish 

 African from American forms by according to them subgeueric rank where there is struc- 

 tural modification sufficient to justify such a proceeding. 



