NO. 1571. DRAGONFLIES OF BURMA AND SIAM—WILLIAMSOX. 279 



than the superior appendages. I. decoratus De Selys occurs in Java, 

 Sumatra, Borneo, and Tonkin. It may be recognized by the asso- 

 ciation of the following characters: Antehumeral yellow stripe 

 slightly or not interrupted; frons black, with a narrow yellow line; 

 a yellow stripe betw^een the two lateral thoracic sutures; posterior 

 edge of side of thorax broadly black; and femora largely brown. 

 7. melsenops De Selys occurs in Indo-China, Sumatra, and Borne©. 

 It is distinct from all by having the antehumeral stripe reduced to a 

 superior spot and the area between the lateral thoracic sutures uni- 

 formly black, or with 1 or 2 small superior spots. Of the remainmg 

 four oriental species (or two species and two varieties) of this group, 

 yertinax Hagen, occurring in China and Tonkin, is separated by having 

 the nasus without a median yellow spot, abdominal segment 8 later- 

 ally spotted, without a yellow ring, and 10 all black. 7. rapax 

 Rambur, known from India and Indo-China, is ver}^ closely related 

 to prsecox Hagen, fi-om India, and mordax De Selys, from India, the 

 latter two being regarded by De Selys as varieties of rapax. I. mor- 

 dax may be recognized from the fact that it has the black stripes on 

 the lateral sutures joined at the middle, reducing the yellow stripe 

 between them to a superior and an inferior spot; as m pertinax, 

 abdominal segment 10 is black. In rapax the abdomen is 47-52 mm., 

 hind wing 40-44 mm.; in prxcox the abdomen is 50-53 mm., hind 

 wing 39-40 mm.; in prxcox the basal black of the frons connects 

 at the middle with the black of the frons in front; in rapax yellow 

 occupies the basal half of abdominal segment 3 and basal two-fifths 

 of 4-6; in precox the yellow is reduced. Closely related as these 

 species are, Hagen' s figures in Monographic des Gomphines indicate 

 differences which should permit of more decisive definitions if material 

 were at hand. 



Second group. — Face largely yellow; posterior edge of side of 

 thorax without black; femora largely yellow. In aiigulosus De Selys, 

 from India, and atrox De Selys, from India, the leaf-like expansions of 

 segment 8 are of medium size, largely or entirely l>lack; in davatus 

 Fabricius, fi'om Japan, China, and Tonkm, and pJialeratus De Selys, 

 from China and Tonkin, the expansion is larger, yellow, broadly 

 bordered with black. In atrox the upper lip is not bordered with 

 black, the rear of the head is black, the expansion of abdominal seg- 

 ment 8 is yellow at the base, and there are 5-6 enlarged spines on the 

 posterior femora; in angulosus the upper lip is bordered with black, 

 the rear of the head is black and yellow, the expansion of 8 is entirely 

 black, and there are 7-8 enlarged spines on the posterior femora. 

 7. plialeratus w^as regarded as a variety of davatus by De Selys, dis- 

 tinguished by a smaller expansion of segment 8, by having segment 10 

 without a dorsal yellow spot, as in davatus, and by having the triangle 

 of the fi'ont wmg followed by 3 cells instead of 4 as m davatus. Three 



