GAD-FLIES (TABANID^) OF THE GENUS STIBASOMA. 



By Frederick Knab, 



Custodian of Diptera, United States National Museicm. 



The genus Stihasoma was established by Schiner for certain Ameri- 

 can species distinguishable from Tabanus by their robust appearance, 

 broad and thick abdomen, long process of the third antennal joint, 

 curved and thickened anterior tibiae, and the broadly ciUate Mnd 

 tibiae. These characters are not equally well developed in all the 

 species of the genus, and there is, on the other side, an approximation 

 toward them in certain species of Tabanus, so that the genus may be 

 said to be a rather weakly defined one. This is shown by the fact 

 that even recent authors have failed to properly place some of the 

 species. Yet the genus seems to represent a natiu'al group. 



The genus is restricted to tropical America exclusive of the Antilles, 

 ranging from Mexico to Uruguay. The position of the species recently 

 described from Austraha by Prof. J. Surcouf, under the name Stiha- 

 soma Tiemiptera (Bigot MSS.), is uncertain and must be excluded, his 

 specimen lacking the antennae.^ The cihation of the legs must be 

 considered a very unimportant character and one that could have 

 been evolved independently in different regions. Indeed, it is devel- 

 oped to different degrees in different species of Stihasoma and in ;S'. 

 fulvoMrtus there is no distinct ciliation on the front and middle 

 tibiae. On the other hand, there is an approach to the condition of 

 the hind tibiae of Stihasoma in certain species of Tahanus, where we 

 find a well-marked cUiation. The condition of the first posterior cell 

 of the wing, which Surcouf seems to consider as diagnostic, is variable 

 in Stihasoma, and in the same species may be slightly narrowed 

 toward the margin or continue of equal width. 



Recently some specimens belonging in the genus Stihasoma were 

 received for identification, and it became necessary to consult the 

 literature on the group. A synopsis was pubhshed by Miss Gertrude 

 Ricardo in 1904,^ in which six species were referred to the genus. 



» Note sur un Dipt^re piqueur du genre Stihasoma Schiner, Bull. Mus. Nat. d'Hist. Nat., 1912, pp. 61-63. 

 2 Ann. Mag. Nat. Hist., ser. 7, vol. 14, pp. 360-362. 



Proceedings U. S. National Museum Vol. 46, No. 2033. 



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