328 NEUROPTERA. 
to the median vein in all, discoidal triangle 2-celled*, internal triangle 3-celled ; three post-triangular 
rows (interrupted by two rows for two or three cells on the left sides, and by two cells on the right 
sides, of the two Altamira males), increasing at the level of the nodus, the post-triangular field hardly 
wider (7 marginal cells, Livingston) or distinctly wider (7-9 marginal cells, Altamira) where it reaches 
the wing-margin, this difference being due to the fact that the first sector of the triangle is more strongly 
curved forward in the Altamira males than in that from Livingston, the highest point of the curve 
in the former coinciding with the interrupting two cells or rows of the post-triangular field mentioned 
above; 8-9 postcubitals, one submedian cross-vein. 
Hind wings with a reddish-brown basal spot, in the subcostal space half-way to (Livingston), or to (Altamira) 
the first antecubital, in the submedian space to the cross-vein (Livingston), or to half-way between cross- 
vein and triangle with a slender limb along the posterior side of the submedian vein to the triangle itself 
(Altamira), and backward to 3 (Livingston) or 7-8 (Altamira) cells beyond the apex of the membranule ; 
7 antecubitals, 8-10 postcubitals, one submedian cross-vein, triangle free, followed by two post-triangular 
cells, two or three single post-triangular cells reaching across the entire width of the field before two 
post-triangular rows begin, proximal side of triangle in prolongation of the arculus, sectors of the triangle 
arising from the same point. 
@ unknown. 
Dimensions of each one of the three males on which this description is based are given in the following order : 
the larger Altamira (type), the smaller Altamira, the Livingston male :—Abdomen 26, 24:5, 21-5; hind 
wing 34°5, 34, 28°5; width of hind wing at arculus 11, 10-5, 9-5; costal edge of stigma of front wing 
3°2, 3°5, 2-5; third tibia 8, 7:5, 6°7 mm. 
Hab. Mexico, Altamira in Tamaulipas (Hoag, coll. P. P. C.: 26); GUATEMALA, 
Livingston (Wilson, M. C. Z.: 1 3). 
Taken at Altamira on June 23 and 27, 1903, at Livingston between February and 
April 1885. 
‘This species differs from the only other described member of this genus, P. ery- 
thropyga, Karsch }, of Uruguay, which has the last antecubital of the front wings not 
continued to the median vein, two submedian cross-veins and only a single post- 
triangular cell reaching across the entire width of that field on the hind wings, a 
longer pterostigma (4~4°7 mm.), a much smaller coloured spot (or none at all) on the 
base of the hind wings, abdominal segments 1—4 (or 5, type ¢ ) pruinose, 5 (or 6)—10 
red, the genital hamule not so prominent as the genital lobe. 
The adult males of Platyplax sanguiniventris, which alone are here described, greatly 
resemble in coloration the adult males of a more common species, Lrythemis peruviana, 
* Not 3-celled, as Tab. IX. fig. 55 represents. 
+ This comparison is based on Prof, Karsch’s description (Ent. Nachr. xvii. p. 270, 1890) and on two males 
from Rio Grande do Sul, Brazil (v. Ihering, A. NV. S.). These males and a photograph of the right wings of 
a male from the same locality, sent to me by Dr. Ris as this species, differ from Prof. Karsch’s description in 
having a small basal brown spot on the hind wings reaching to the submedian cross-vein and backward to the 
apex of the membranule. The original description mentions no such spot, and Dr. K. Griinberg, who kindly 
re-examined the types at my request, wrote (29.ix.05): “ bei Platyplax erythropyga, Karsch, 3 @ , die Fliigel 
absolut farblos und wasserhell sind.” 
The two Rio Grande do Sul males and Dr, Ris’s photograph show some other differences from the description 
of erythropyga as follows: sectors of the arculus not stalked at origin on the front wings; hind wings with 
one and two asymmetrically submedian cross-veins, or with one cross-vein only ; sectors of triangle separated 
at origin on both sides of one male. 
