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Psyche 
[Vol. 92 
In the most recent key to North American genera, Pechuman and 
Teskey (1981) used the absence of a spur vein on the fork of the R 4 
and R 5 veins, eyes bare in both sexes, the rounded female cerci and 
projecting process of the male gonostylus to separate Stonemyia 
from Pilimas. Except for genitalic differences, these characters will 
not always reliably separate these genera. 
Mackerras (1955) discussed differences in the genitalia of Stone- 
myia and Pilimas. In females, Pilimas has a prominent apical lobe 
on the cerci (strongly bilobed in californicus ) and the caudal ends of 
spermathecal ducts are membranous and unexpanded, while Stone- 
myia has cerci without an apical lobe and the caudal ends of the 
spermathecal ducts expanded and sclerotized. The gonostylus of 
Stonemyia has a peculiar outwardly projecting wing that is absent in 
Pilimas males. 
The importance of male and female genitalia in generic separation 
of Stonemyia and related genera needs to be re-examined. Because 
tabanid genitalia are relatively simple and unspecialized, their struc- 
tural features usually have not been useful for determining relation- 
ships below the level of tribe, but such features as are present should 
be examined critically at the generic level to determine if they can be 
used reliably to separate closely related genera. 
Several years ago, J. R. Vockeroth of the Biosystematics 
Research Institute, Ottawa, discovered an interesting character in 
certain species of Stonemyia that appears to be unique in Tabani- 
dae: the presence of a row of erect bristles on the ventral surface of 
the scutellum. I examined the North American species of Stonemyia 
in the collection of the U.S. National Museum and Stonemyia 
yezoense (Shiraki) from Japan and found that both sexes of all 
species possessed the bristles, although sometimes they were diffi- 
cult to see because the base of the abdomen was closely appressed to 
the ventral area of the scutellum. 
All other genera of Tabanidae in the USNM collection had the 
ventral surface of the scutellum bare, except both sexes of Pilimas 
californicus, which had strong bristles on the ventral surface of the 
scutellum as in Stonemyia species. The other two species of Pilimas 
( P . abaureus Philip and P. ruficornis (Bigot) have the ventral sur- 
face of the scutellum bare and also differ from Stonemyia species in 
having the subscutellum conspicuously inflated, whereas in Stone- 
myia it is only slightly enlarged and much less conspicuous. The 
