40 NORTH AMERICAN DIPTERA. 



naked and free, from which extend eight or sixteen very long, 

 slender, threadlike breathing tubes. The perfect insect es- 

 capes under water and comes to the surface. The larvae are 

 soft-skinned, thickened at the extremities, with a cylindrical 

 head, two pairs of eyespots; on the first thoracic segment 

 there is a foot protuberance with bristly hooklets ; and the 

 end of the abdomen has several appendages for attachment. 

 But one genus is known in the family, Simulium, which 

 will be recognized from the characters already given. 



12. EHYPHIM:. 



Head nearly hemispherical ; eyes rounded, holoptic, or 

 nearly so in the male ; broadly separated by the front in the 

 female ; ocelli present. Antennae aboiit as long as the thorax, 

 composed of sixteen joints, cylindrical, the two basal joints 

 distinctly differentiated; those of the flagellum closely united, 

 short-haired, gradually decreasing in size toward the end. 

 Proboscis moderately prominent, with sinall labella ; palpi 

 very long, four-jointed ; the second joint longer and broader 

 than the others. Thorax convex, without transverse suture ; 

 scutellum semicircular, short and broad; metanotum strongly 

 developed. Abdomen cylindrical, composed of seven seg- 

 ments; genitalia concealed or nearly so. Legs slender, with- 

 out spines; the coxae, especially the front pair, more, or less 

 elongated; metatarsi elongated; tibiae without spurs or the 

 hind pair with minute ones ; empodia pad-like, the pulvilli 

 absent. Wings large, in rest lying flat upon the abdomen ; 

 auxiliary vein present; the costal vein reaching to the tip 

 of the third vein. Discal cell present, from which three 

 veins originate, and a fourth arises from the posterior basal 

 cell ; five posterior cells and two elongated basal cells present ; 

 a distinct stigma. 



But very few species of this family are known, belonging 

 to but two or three genera. The typical genus Rhyphvs con- 



