4 MISC. PUBLICATION 305, U. S. DEPT. OF AGRICULTURE 
the Bellardiinae, is frequently not even of generic value, and the 
shape of the basal portion of the third antennal segment, when used 
alone, is rarely of even generic value. For the purposes of a tax- 
onomic study of the entire family some of the more restricted sub- 
families are undoubtedly desirable, but for this revision the writer 
prefers to interpret the subfamily more broadly as Brennan has done 
in the case of the Pangoniinae. It is the writer’s opinion that be- 
cause superficial characters have been utilized for separating the 
larger groups of Tabanidae, much of the present classification ob- 
scures rather than elucidates the true relationships. The Tabanidae 
show unusually little variation of a fundamental character, and a 
great deal more must be learned of the morphology and biology, 
particularly of the immature stages, before a satisfactory natural 
classification can be attained. | 
CHARACTERS OF VALUE AND THEIR TERMINOLOGY 
There is a decided paucity of structural characters in the Taba- 
nidae, and the few present are nearly all confined to the head. 
Macrochaetae being absent, chaetotaxy- cannot be utilized. The wing 
venation is relatively constant throughout the subfamily Tabaninae, 
and what modifications there are tend to be inconstant within a 
species. Because structural characters are few and because many of 
the cephalic characters are confined to the female, it is necessary to 
depend on coloration to a considerable extent. 
TINCTORIAL CHARACTERS 
The eye pattern is usually found only in fresh or relaxed speci-. 
mens, the frequently brilliant color fading shortly after death and 
eventually disappearing. This must be remembered when the de- 
scriptions are being read. Pollinosity, as used in this publication, 
means any fine dusting over a surface regardless of its color. Unless 
otherwise stated, body coloration is the color of the pollinose surface. 
The presence or absence of pollen is frequently of taxonomic im- 
portance. The abdominal pattern is of greatest value and serves to 
separate the genus Z’abanus into rather well defined groups. 
CEPHALIC CHARACTERS 
The term frons is here applied to that portion of the head between 
the eyes and from near the top of the head to the lower, inner angle 
of the eyes. Morphologically the frons is marked above by the 
position of the median ocellus, when present, and below by a suture 
just below the antennae, but for the part below the levei of the 
lower, inner angle of the eye the writer retains the descriptive term 
subcallus. In the male the frons is reduced to a very narrow triangle 
below the eyes, which, combined with the subcallus, the writer calls 
the frontal triangle. The term vertex is used here for the top of 
the head between the eyes. Frequently a tubercle is present on the 
vertex at a point corresponding to the position of the ocelli in many 
Pangoniinae. This has been called the ocellar tubercle or ocelligerous 
