496 PROCEEDINGS OF THE NATIONAL MUSEUM VOL. 113 
of Amoebaleria and Heleomyza. An attempt is made here to give 
added emphasis to the male terminalia and in certain cases to use 
them as a basis for taxonomic discrimination. I have followed 
Crampton and others (1942, p. 76) in using “terminalia” for indicating 
the genital and post-genital segments, and have adopted the termi- 
nology used by Steyskal (1957) for the component structures. The 
male terminalia are not always symmetrical; therefore, the figures 
drawn from the left side will not compare exactly with specimens 
viewed from the right side of the insect. Most of the figures were 
drawn from cleared specimens, with the result that spines, setulae, etc. 
which occur on the medial side of a structure may appear in a lateral 
view of that structure. Because it is usually necessary to clear the 
terminalia before examining them, this method of illustration makes 
the figures coincide more closely with the actual appearance of the 
specimens. 
The cheek-eye ratio had been utilized previously to a very limited 
extent in heleomyzid taxonomy, but in certain genera it seems to have 
some value in species discrimination. The ratio was obtained through- 
out the present study by viewing the head in lateral profile and by 
measuring the greatest vertical height of the cheek (usually along the 
posterior margin), which was then divided by the greatest vertical 
height of the eye. 
Family limits have been variously placed with respect to the 
Heleomyzidae, Trixoscelidae, and Chyromyidae. Czerny (1927a) 
advocated treating both the Trixoscelidae and Chyromyidae as sub- 
families of the Heleomyzidae, although in his 1924 monograph he 
included the Heleomyzidae only in the strict sense. Curran (1934) 
included the Trixoscelidae as a part of the Chyromyidae and separated 
both from the Heleomyzidae. 
The Chyromyidae differ in several basic characters from both the 
Heleomyzidae and Trixoscelidae, namely in having poorly developed 
oral vibrissae (Collin, 1943, doubts that they are homologous with 
the oral vibrissae of the other groups), poorly developed costal spines, 
and no dorsal preapical bristles on the tibiae. These differences may 
be considered sufficient grounds for excluding the Chyromyidae from 
the Heleomyzidae. 
The Trixoscelidae were separated from the Heleomyzidae and 
treated as a distinct family by Frey (1921), Hendel (1928), Séguy 
(1950), and Melander (1952). Czerny (1927a), Malloch (1930), 
Collin (1943), and Colyer and Hammond (1951) united the two 
groups under the Heleomyzidae. The Trixoscelidae differ from the 
Heleomyzidae in having the ocellar bristles placed laterad to the 
fore ocellus rather than between the fore and hind ocelli. They 
differ further in having frontal plates which reach the frontal suture, 
