8 CYRTIDAE OF NORTH AMERICA 



The alulae vary in size; the thoracal squamae are always large 

 and are one of the striking characters of the family, the margins 

 being thickened and with a fringe, in some forms with a hairy 

 surface. The alar squamae are not abnormally developed, with 

 a short fringe or bare. The halteres are small and entirely cov- 

 ered by the bulging squamae. 



The venation is very important, although the classification 

 cannot be based on this alone, as has been proven. Lasia, which 

 is represented in the United States by two species, has a venation 

 very near the Nemestrinidae (see Plate I, fig. I). In Hirmo- 

 neura (Nemestrinidae) the discal cell is absent but otherwise the 

 venation corresponds to Lasia. Verrall says: "It would appear 

 that an absolutely different principle has been adopted (in two 

 allied groups) to strengthen the wings; in the Nemestrinidae by 

 tying the elongate end veins together, but in the Cyrtidae by 

 connecting the anterior and posterior parts of the wing by a 

 strong tie near the base and also (in Lasia, etc.) by a second 

 tie near the end of the wing." When the Cyrtidae adopted the 

 floating flight which some of them have, the second tie was 

 allowed to die out and the outer veins to become obsolete. The 

 venation of Eulonchus is very near Lasia, but the third longi- 

 tudinal fork is less like the Nemestrinidae and the axillary vein 

 is not so strong. 



Thyllis gives a clue to the venation of Oncodes and Acrocera. 

 The fork of the third longitudinal vein has disappeared and, in 

 one species of that genus {T. crassus), the third veinlet from the 

 discal cell has been obliterated , thus there is no closed fourth pos- 

 terior cell. In T. tristis the third vein seems to exist and is a 

 continuation of the fifth longitudinal vein which has disappeared. 

 The venation of Ptero-pexus is near that of Eulonchus. Opsebius 

 (Plate I, fig. 8) and Cyrtus have a venation very near alike; the 

 third longitudinal fork is still present in these two genera. There 

 is quite a variation in the former; in some the anal cell is closed 

 and petiolate and in others wide open. Perhaps the venation of 

 Opsebius is a modification of that of Cyrtus. Loew in figuring the 

 wing of Opsebius inflatus left out the characteristic cross-vein 

 which forms the outer first basal cell; Ostcn Sacken discovered 

 this in examining the type. The venation of Ocnaea (Plate I, 

 fig. 3) is very near that of the South American Holops and varies 



