362 NORTH AMERICAN DIPTERA 



Family Clusiidae 



Rather small flies in which the wings are almost always marked 

 with black or brown. 



Head broad, sub-hemispherical; face short, nearly vertical or gently 

 receding below; front broad, with three or four pairs of frontals and 

 often with a pair of cruciate interf rontals ; ocellars present or absent; 

 postverticals divergent, rarely absent. Antennge porrect, the basal two 

 segments short, the third rounded, with a terminal or subapical arista 

 which may be bare, pubescent, or thickly long haired. Proboscis short, 

 the palpi rather broad. Abdomen of moderate length, rather slender. 

 Legs of moderate length, slender, the tibiie with or without a preapical 

 bristle. Wing venation complete, the second basal and anal cells very 

 small; first vein ending near the basal fourth of the wing, the auxiliary 

 vein narrowly separated from it. 



The adults are found in moist places and about decaying wood, 

 sometimes occurring in large numbers, although most of the species are 

 not common. 



The larva? occur in decaying wood and under the bark of trees. 

 They are white, slender, cylindrical and slightly thickened posteriorly. 

 Mouth hooks small, the segments not distinctly separated but with trans- 

 verse ventral swellings for locomotion. They have the power of leap- 

 ing, accomplishing this by grasping the booklets on the apical segment 

 Avith their mouth hooks and suddenly letting go. The puparia are 

 yellowish, ellipsoidal and with horns on the a])ical segment as in the 

 larvffi. 



]\Ielander and Argo* have revised the American species of the 

 family including many species from other regions. The vast majority 

 of the species are tropical. Of the seventy known American species 

 only a small number occur in the Nearctic region. 



KEY TO GENERA 



1. Eyes with microscopic pubescence; costa broken near the humeral 



crossvein (8, 11) Acartophthalmus Czerny 



Eyes bare; costa weakened or broken near the end of the auxiliary vein. 2 



2. Anterior pair of frontal bristles convergent or proclinate 4 



All the frontal bristles reclinate S 



Proc. U. S. N. M.. 1924. Vol. xliv. Article 11, pp. 1-54. 



