FAMILY CHLOROPID.E THE FRIT FLIES 341 



boscis is nothinj? more than the labellaj which are lengthened and 

 narrowed and it is not always easy to decide whether the proboscis is 

 geniculate or not. Trouble will also be experienced in connection with 

 the pubescence of the arista and the presence of frontal bristles, both 

 of which are characters which show gradual development in the pres- 

 ence of extensive collections. The only revision of the North American 

 species of this family is by Becker.* In a recent paper on the Neotropi- 

 cal forms Diidat has proposed many new genera but his contril)ution 

 has been so badly mangled by deletion necessitated in order to reduce 

 its size to the absurd limits set by most publications that it is almost 

 impossible to follow his keys. 



KEY TO GENERA 



1. Costa extending to the fourth vein 11 



Costa ending at the third vein or slightly beyond it 2 



2. Posterior crossvein absent Elliponeura Lcew 



Posterior crossvein present 3 



3. Posterior femora greatly thickened, their tibiae strongly arcuate 



(4, 17) Meromyza Meigen 



Posterior femora only moderately thickened, their tibiae but little 

 curved 4 



4. Middle tibiae with a strong, curved apical spur; male genitalia large, 



carried forward under the abdomen (6, 14, 21) Cetema Hendel 



Middle tibiae with normal terminal bristles 5 



5. Posterior tibise with an oval, opaque "sensory organ" posterodorsally, 



the tibiae somewhat broadened (18, 23, 26) Chloropisca Lcew 



Posterior tibae without velvety sensory area 6 



6. The distance between the crossveins along the fourth vein is not 



greater than the length of the posterior crossvein (11). . Diplotoxa Lcew 

 The distance is equal to at least twice the length of the posterior 

 crossvein 7 



7. Mesonotum entirely black, coarsely punctured Ephichlorops Becker 



Mesonotum usually vittate, not wholly black nor coarsely punctured. . . 8 



8. Third antennal segment conspicuously longer than broad 9 



Third segment rather circular in outline, often broader than long, 



never conspicuously longer than broad (2, 3) Chlorops Meigen 



9. Frontal triangle shining 10 



Frontal triangle opaque (28) Anthracophaga Lcew 



10. Frontal triangle very long and broad, ending in a broad, obtuse point 

 a little before the base of the antennae, convex in cross-section 



(12, 24) Ectecephala Maccjuart 



Frontal triangle strongly narrowing anteriorly and ending in an acute 

 point, flat in cross-section (16, 25) Parectecephala Becker 



« 1912. Ann. Mas. Nat. Hung., x. pp. 21—. 

 t 1930. Fol. Zool. Hydrobiol.. ii. pp. 46-128. 



