MICRATHYRIA. 221 
Dr. Ris® states that about fifteen species of Micrathyria, as here limited, are known 
to him. They are restricted to the present faunal district, the West Indies, and South 
America. A characteristic feature of the females is the shortness of the ninth and 
tenth abdominal segments in proportion to their width. 
Some of our present species approach each other very closely *. 
Key to the Mexican and Central-American Species. 
A. Number of cells between the posterior angle of the triangle, hind wing, and the 
distal subbasal sector (A, of Comstock and Needham) immediately opposite that 
angle ¢wo, internal triangle of front wing 3-celled. g. Superior appendages 
with no inferior subbasal denticle. 
B. Discoidal triangle of front wing 2-celled. 
C. Post-triangular field of hind wing with no single cell reaching from short 
sector to first sector of triangle. Brown stripe on obsolete first lateral 
thoracic suture (i. e. at the metastigma) not forked, no brown metepimeral 
stripe. . Anterior lamina bifid to base, apices narrower (viewed in 
profile), not spinulose; hamule more prominent than adjacent parts, its 
much longer outer branch curved forward, apex flattened, wider, trans- 
versely truncated, denticulated, the short spine-like inner branch pointing 
backward. @. Vulvar lamina reaching to one-half the lateral margin of 
segment 9, not attaining the bases of the ventral style-like processes, its 
apical margin excised or bilobed for its whole width, the two sides of the 
excision forming an angle of about 110°; style-like processes of 9 about 
-2 mm. long, one-fifth as long as the lateral margin of that segment. 
Abdomen, ¢ 22°5-29, ? 20-25; hind wing, g 26-38, ? 25-30 mm. . 1. didyma. 
CC. Post-triangular field of hind wing with at least one cell reaching from 
short sector to first sector of triangle. Brown stripe on obsolete first 
lateral thoracic suture forked in its upper half, a brown metepimeral 
stripe running off from near the lower end of the second lateral thoracic 
suture, antecubitals on hind wing 7-9. ¢. Anterior lamina as promi- 
pent as genital lobe, its apex biparted, each tip spinulose ; hamule a little 
more prominent than the other parts, hook-like, directed backward ; 
superior appendages in dorsal view with their tips pointing almost 
straight backward, in profile view with an inferior tooth at two-thirds 
their length, distal side of tooth forming almost a right angle with 
appendage, proximal side forming a much more oblique angle with the 
appendage and bearing five denticles, no external row of denticles. 
Abdomen, ¢ 27-28, 9?; hind wing, ¢ 32-36,?? 325mm... . . 2. atra. 
* It is much to be regretted that recent authors, in introducing new species of Micrathyria, have not 
followed the example, set by Hagen in 1861, of describing the external genitalia, which are unquestionably the 
chief specific characters in this genus. The difficulties of identification are much increased by this omission. 
BIOL. CENTR.-AMER., Neuropt., April 1906. 9d g 
