A REDEFINITION OF STONEMYIA (DIPTERA: TABANIDAE) AND DESIGNATION OF A NEW GENUS, PEGASOMYIA, FROM WESTERN NORTH AMERICA

The genus Stonemyia was erected by Brennan (1935) to receive North American pangoniine species previously assigned primarily to non-Nearctic genera. Brennan placed species with bare eyes in Stonemyia s. str. For species with pilose eyes, at least in the male, he proposed the subgenus Pilimas. He did not, however, fix a type for Pilimas as required by the International Code of Zoological Nomenclature for genus-group names proposed after 1930. Pilimas, therefore, was unavailable. Pilimas was raised to the generic level by Philip (1941 a) and Brennan subsequently (in Philip, 1941 b) designated Diatomineura calfornica Bigot as the generotype of Pilimas in a note at the end of Philip’s paper.

Pilimas as required by the International Code of Zoological Nomenclature for genus-group names proposed after 1930. Pilimas, therefore, was unavailable. Pilimas was raised to the generic level by Philip (1941 a) and Brennan subsequently (in Philip, 1941 b) designated Diatomineura calfornica Bigot as the generotype of Pilimas in a note at the end of Philip's paper.
Structurally, both genera are very similar. Authors treating them have used primarily the presence or absence of a spur at the fork of the R4 and R5 veins and whether the eyes are bare or pilose. Neither of these characters, however, will absolutely separate these genera. Differences in the male and female genitalia have been used less frequently, perhaps because it is difficult to interpret structural differences observed.
Middlekauff and Lane (1980) summarized the morphological differences between Stonemyia and Pilimas, but did not mention genitalic differences. In their key, only the presence of the spur vein in Pilimas and its absence in Stonemyia is used to separate them. However, in their discussion of generic differences, they state that 5% of Pilimas californica (sic) lack the spur vein. They also mention that the eyes of Pilimas are "slightly" hairy and that those of Stonemyia are "practically bare." 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 R4 and R5 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 Stonemyia and Pilimas. In females, Pilimas has a prominent apical lobe on the cerci (strongly bilobed in cal[brnicus) and the caudal ends of spermathecal ducts are membranous and unexpanded, while Stonemyia 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 Stonem),ia and related genera needs to be re-examined. Because tabanid genitalia are relatively simple and unspecialized, their structural features usually have not been useful for determining relationships 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 Stonem.via that appears to be unique in Tabanidae: the presence of a row of erect bristles on the ventral surface of the scutellum. 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 difficult 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 cai([brnicus, 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 surface of the scutellum bare and also differ from Stonemyia species in having the subscutellum conspicuously inflated, whereas in Stonemyia it is only slightly enlarged and much less conspicuous. The shape of the body of cal([brnicus is similar to the bee-like appearance of the Stonemyia species, the abdomen being stouter and more rounded, compared to Pilimas abaureus and ruficornis, whose abdomens are more slender and more nearly parallel-sided. therefore believe that cal(Ibrnicus was mistakenly placed in the genus Pilimas and belongs instead in Stonemyia. Since Brennan designated cal([brnicus as the generotype of Pilimas, a new name is needed in which to place abaureus and rufl'cornis. Pegasomyia, new genus, is hereby proposed and contains these two species. The name is taken from Pegasus, the legendary flying horse of Greek mythology. Pilimas becomes a synonym of Stonemyia, rw SVrOr'M,.
Six Palaearctic species have been placed in Stonemyia: yezoense (Shiraki), enokizonoi (Ouchi), hispanica (Krober), caucasica (Krober), tigris (Bigot) and bazini (Surcouf) (=chekiangensis (Ouchi)) (Moucha, 1976;Leclercq and Olsufjev, 1975). Stonemyia yezoense is a well-known Japanese species and has bristles beneath the scutellum as do the North American species. St. caucasica has well-developed ocelli and could be a Stonemyia species but this needs to be confirmed. The type male of St. enokizonoi, collected from Yaku Island off the southern coast of Japan, is thought to have been destroyed in Shanghai, China during World War II (Hayakawa, personal communication). It is very close to St. yezoense and may be conspecific with it. Study of hispanica by Schacht and Portillo (1982) revealed that it is a species of Philoliche (Ommatiosteres), not Stonemyia. Chainey (1983) provided a complete description and discussion of P. hispanica. It seems unlikely that tigris should be placed in Stonemyia since Bigot mentions in his original description that ocelli are absent, whereas they are welldeveloped in all known Stonemyia species. It is possible that tigris Psyche [Vol. 92 may also prove to be a species of Philoliche. Moucha (1976) listed bazini as a species of Philoliche, but this is unlikely since Surcouf (1922) described it as having well-developed ocelli and posterior cells of the wing wide open. Leclercq and Olsufjev (1975) list it in Stonemyia, but this should be confirmed by examination.
Thus, in the Palaearctic Region, only yezoense has been definitely confirmed as belonging in Stonemyia, but bazini and caucasica may also belong there.