AET. 11. FLIES OF THE FAMILY CLUSUDAE MELANDER AND AEGO. 3 



deliaii recombination within a single species, require the services 

 of some future experimental geneticist; but in view of the great 

 rarity of specimens in this family the conclusions advanced in the 

 following pages are given as a taxonomist's solution. A "splitter," 

 disregarding the evidence produced by breeders of Drosophila, would 

 find opportunity in many cases, especially with the tropical forms, 

 to erect a new species for almost every individual, and still not 

 exceed species characters accepted in other groups. 



Chaetotaxy is important in identifying the different genera. At 

 first it would appear that the genera are based too closely upon 

 permutations of a few bristle characters, and hence are purely 

 artificial concepts. However, the degree of development of such 

 bristles as the fronto-orbitals, cruciate frontals, ocellars, postverti- 

 cals, prothoracic, dorsocentrals, preapical tibials, and bristles on 

 the first vein, leads to the primary separation of species into groups 

 that may be regarded as natural genera. Williston has doubted 

 the appropriateness of some of these chaetotactic genera, and in 

 his North American Diptera has questioned the validity of characters 

 like the preapical or cruciate bristles. The removal of Williston's 

 species Heteroneura lumhalis and H. valida from Heteromeringia to 

 SoharocepTiala straightens out the seeming discrepancy and stabilizes 

 all three genera. 



The substance of the present review was presented by Mrs. Argo 

 to satisfy the thesis requirement for the degree of master of science 

 in zoology at the State College of Washington. With the inclusion 

 of subsequent material the senior author has rewritten the paper 

 and shares equally in the responsibility of its presentation. We 

 express herewith due appreciation and gratitude to Dr. J. M. Aldrich 

 for forwarding the unworked Clusiidae of the United States National 

 Museum, to Dr. O. A. Johannsen for the loan of the Cornell material, 

 including cotypes of some of Williston's species, and to R. C. Shannon, 

 who had anticipated monographing this family but who kindly 

 relinquished his aggregated material. It was Mr.Shannon's request 

 that we carry on his project that served as the first stimulus for 

 undertaking this review. To Maj. E. E. Austen we also record 

 gratefulness for information regarding types in the British Museum. 



The photographs for the plates were made by the senior author, 

 using a Zeiss IC Tessar lens of 12 cm. focus, stopped to f/25. With 

 a 4-foot camera the initial magnification was almost ten times. 

 The specimens were lighted by a 400-watt stereopticon bulb, and 

 were given a 5-minute exposure on Orthonon plate. To bring out 

 the neuration and chaetotaxy they were given a supplementary 

 silhouetting exposure of 20 seconds, using a substage microscope 

 lamp placed directly behind the specimen. Even with the ortho- 



