308 ME. W. F. IUKBY— A REVISION OF 



triangular nervure, one cross nervure in the lower basal cell, sectors of the triangle 

 widely separated at their origin : anal appendages of the male short and straight. 



Type Libellula tetra, Ramb. 



This genus will include all the species placed in Biplacina by Brauer, except his type, 

 D. nana, from the Philippines, which is clearly not congeneric with the others. Several 

 species previously referred to Diplaoc will come better here, such as Libellula nebulosa, 

 Fabr. (E. Indies), Diplax exul, Selys (S. Africa), and Lib. minuscula, Ramb. (S. America). 

 In the smaller species (Diplacodes minuscula and nebulosa) the triangle of the fore wings 

 occasionally shows a tendency to assume a trapezoidal form, as in Nannopkya, &c, owing 

 to the lower sector of the arculus sometimes, but only occasionally, falling on the base 

 of the triangle before its extremity. 



Genus 76. Diplacina. 

 Brauer, Verb, zool.-bot. Ges. Wien, xviii. pp. 173, 368, 733 (1868). 



Brauer's typical species is not before me ; but it differs sufficiently from Diplacodes 

 by the following characters : — Fore wings with the pterostigma short and broad, 12 

 antenodal and 8-9 postnodal nervures, triangle free, followed by first two, then one, 

 and then two or three rows of cells, subtriangular space divided by a curved nervure, 

 one supratriangular nervure. 



Type Biplacina nana, Brauer. 



Genus 77. Acisoma. 



(Neuration, Plate LVI. fig. 5.) 



Rambur, Ins. Nevr. p. 28 (1842) ; Brauer Verh. zool.-bot. Ges. Wien, xviii. pp. 367, 724 (1868). 



Frontal tubercle convex above; eyes contiguous in the middle; abdomen as long as 

 the hind wings, segments 2-4 carinated, segments 1-5 broad, but cylindrical, and not 

 inflated, the remaining segments suddenly tapering, and comparatively slender, segment 

 8 not perfoliate in female : wings and pterostigma moderately long ; fore wings with 

 6-8 antenodals, the last continuous in the type but not in other species, and 6-8 post- 

 nodals, the first two not continuous, cells of the postnodal area simple, triangle mode- 

 rate, tree, on a level with that of the hind wings, and followed by two rows of cells, no 

 supratriangular nervure, one cross nervure in the lower basal cell, subtriangular space 

 consisting of one or three cells, sectors of the arculus stalked, more or less gradually 

 curved, nodal sector undulating at the base, subnodal continuous, the intermediate 

 cells only bisected (if at all) on the extreme margin ; hind wings only slightly broader 

 than the fore wings, with 5-7 antenodals and 6-8 postnodals, the first two postnodals 

 not continuous, triangle open, followed by three rows of cells, no supratriangular 

 nervures, one cross nervure in the lower basal cell, sectors of the triangle widely sepa- 

 rated at their origin : anal appendages of the male hardly longer than those of the 

 temale ; four hind tibise armed with a double row of about seven strong spines. 



Type Acisoma ascalapthoides, Ramb. 



