38 Revista de la S. E. A. (N.o 6 — 1928) 



The gemís Microdon itself offers a splendid example of a very 

 plástic morphologieal gronp. It is very rich in species, whieh show 

 a great variety of t'orm, color and structiiral differenees. In spite of 

 this great diversity of differenees, workers have found it most iinsa- 

 tisfactory to attempt to divide the groiip, even to the point of ma.king 

 tangible subgenera and consequently all of the American and prac- 

 tically all of the oíd world forms are retained under the single ge- 

 neric ñame, Micvodon. Even such a remarkable eharacter as the com- 

 plete loss of an abdominal segníent Avhich a certain species of the 

 gemís Microdon, namely Microdon lactipennis Shannon, shows has 

 been eonsidered as only a specific eharacter. We woiild expeet that 

 ihe complete loss of a segment woiild indícate at least a generic dif- 

 ference (possibly a faraily difference) espeeially as no other species of 

 the Syrphidae have the a^bdoininal segments reduced to such a small 

 nmnber. In this case, the species is so obvionsly a member of tlic 

 group ühristes, that there would be nothing gained by plaeing it in a 

 genus of its own, and certainly to make it the type of a group higher 

 than agenus (tribe or sul)family) would be very unfortunate. The 

 group rhristes is peculiar in that it rcsembles the stingless honey bees, 

 genus Trígona, but aside froin this resemblance, a>nd an unusal number 

 of striking characters (wliich I considered purelj^ specific) it shows no 

 common morphologieal eharacter whereby it can be separated froiii the 

 other members of the gemís Microdon even as a subgenus. Even Ma- 

 íiarygua planifrons is no more peculiar in its way, than are the species, 

 of Uhristcs. 



Finally, it has come to be a recognizecl procedure among entomo- 

 logists not to créate genera on the basis of sexual characters alone (as 

 was done in the case of Masarygus Bréthes) and until doctor Bréthes 

 demonstrates that the female as well as the niale is generically dis- 

 tinct from the other species of Microdon on the baisis of a eharacter 

 common to botli of them, the so-called gemís Masarygus will not be 

 accorded generic rank by the eníomological profession. 



Certainly. it does not represent a clifferent fa-mily from tlie Syr- 

 phidae, as it was described by Dr. Bréthes. 



Recently, another species with a divided third antennal joint 

 (similar to that of Masarygus planifrons Bréthes) has been described 

 from Australia, under the ñame Microdon alcicornis Ferguson (Revi- 

 sión Australian Syrphidae, part I, 1926). 



Ferguson remarks : ' ' The antennal structure is most extraordinary 

 biit I do not think this sufficient to justify the erection of a new ge- 

 nus, as in all other respects the species is in aigreement with other 

 Australian species of Microdon and the antennae are most variable 

 in this gemís". 



