40 XOrvTII AMEPJCAN DIPTEKA. 



iiakeil and free, from which extend eiglit 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^ tlie extremities, with a cylindrical 

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

 there is a foot protuberance with bristly booklets; and the 

 end of the abdomen has several appendages for attachment. 

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

 will be recognized from the characters already given. 



12. RHYPHID.E. 



Head nearly hemispherical ; eyes rounded, holoptic, or 

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

 female; ocelli ])resent. Antennte about as long as the thorax, 

 composed of sixteen joints, cylindrical, the two basal joints 

 distinctly differentiated ; those of the flagellum closely united, 

 short-haii*ed, gradually decreasing in size toward the end. 

 Proboscis moderately prominent, with small labella ; palpi 

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

 than the others. Thorax convex, without transverse suti;re ; 

 scutellum semicircular, short and broad; metanotum strongly 

 developed. Abdomen , cylinctncal, 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 ; em})odia pad-like, the pnlvilli 

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

 auxiliary vein present; tlie costal vein reaching to the tip 

 of the third vein. Discal cell present, from which t\\vev. 

 veins originate, and a fourth arises from the jjosterior basal 

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

 a distinct stigma. 



But very few species of this family arc known, belonging 

 to but two or three genera. Tlic typical genus Rlini'lnis con- 



