Tabanidae of Nebraska 3 



Silvius Meigen 



There are but five known North American species in this 

 genus, one of which is here described as new. Two of these 

 five species are known to occur in Nebraska. In order to 

 show the relationships of the new species, the following key to 

 all five of the North American species is ofifered : 



1. Wings blackish, costa more intense jonesi 



Wings hyaline, with or without spots 2 



2. Wings without spots, whole body yellowish 3 



Wings usually spotted, whole body grayish 4 



3. Abdomen uniformly yellow with a dark spot beneath the scutel- 

 lum and an elongated spot of the same color in the middle of the 

 second segment; denuded areas on face; length 9, 10-12 mm. 

 gigantidiis 



Abdomen not uniformly yellow, no denuded areas on face; 

 length 9 , 10-11 mm microcephalus 



4. Abdomen with four longitudinal rows of spots; length $ $, 

 6-10 mm quadrivittatus 



Abdomen with two longitudinal rows of spots; length 9, 10 

 mm pollinosus 



Silvius microcephalus n. sp. 



9. Length 10-11 mm. In coloration this species approaches gigan- 

 tulus, except that it is paler. The head appears small in comparison to 

 the rest of the body, and the abdomen is broad. Face and front grayish- 

 pollinose, sparsely covered with pale yellow and black pile; no denuded 

 areas on face as in gigantulns. Front narrow; frontal callosity small, 

 black and round; ocelli ruby-colored; ocelligerous tubercle of the same 

 color as the front. Proboscis shorter than the head. Antennae with 

 first two joints yellow, beset with short black hairs, the basal annulus 

 reddish-yellow, the apical four annuli black. The antennae is but little 

 longer than the proboscis. The thorax is yellowish-poUinose, darker than 

 either the face or the abdomen, with pale and black pile associated to- 

 gether, and with three longitudinal faint mesonotal vittae. Scutellum 

 of the same color as the thorax. Abdomen broadly yellow on the sides, 

 leaving a broad black stripe in the middle on which is a row of small 

 faint gray triangles, the apex of that on the second segment reaching 



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