MICRODON, 119 
Genus 25. MICRODON, Mergen (1803). 
In the case of this genus the collection includes very many 
interesting species, the majority of which are strikingly coloured, 
while some appear to mimic various species of Hymenoptera. The 
differences in structural characters are so pronounced that separation 
into minor genera seems to be necessary; this, however, is not easy, 
because the shape of antennz is very variable and shows gradual 
transition to the extreme forms; the scutellum also gradually 
passes from the armed to the unarmed form. 
Of the generally accepted genera, Ceratophya, Myxogaster, and 
Rhopalosyrphus are exclusively American, and therefore need not 
be considered here. In the collection, however, there is a mutilated 
specimen from the Cape which closely resembles -Wyxogaster or 
Rhopalosyrphus, but has two small spines on the scutellumn ; 
Dr. J. C. H. de Meijere, again, has described three Oriental species 
(vespifor mis, indicus, and odyner -oides ), whichexhibit the characters 
of the genera mentioned, while in each case the scutellum is 
unarmed. 
The recently described genus Paramicrodon, de Meijere, 1913, 
which oceurs in New Guinea, has short antennz and an unarmed 
scutellum, and is distinguished by the absence of a stump on the 
third yein. 
Of the generic names relegated to synonymy, Chymophila 
pain to have been applied to a Microdon with the head of a 
onops glued upon it; Dimeraspis was bestowed upon a true 
North. American Microdon not far removed from the European 
forms, but with an unarmed scutellum ; MJesophila is merely a 
nomen nudum, which also applies to a North-American species of 
true Microdon, with bilobed scutellum; Udbristes was bestowed 
upon a Neotropical species, and, although its characters were not 
clearly defined, it was possibly meant to include South-American 
forms with an unarmed scutellum; Omegasyrphus also includes 
American forms with: narrow abdomens, the second segment of 
which exhibits a very peculiar sculpture. 
As stated above, the Ethiopian forms before me exhibit a 
great many structural variations, the existence of which renders it 
necessary to institute new genera; for the present, however, it seems 
better to divide the species in question into anonymous groups, 
since some of the names mentioned above can perhaps be apphed 
to them. I have introduced only two new generic names for two 
very striking forms, one of which is allied to Ewmerus and has 
been described above. 
The following is a table for the distinction of the Ethiopian 
groups of the genus Mierodon, s. 1., with the addition of the twe 
new genera :— 
1 (14) Middle cross-vein situate on the basal third of 
the discal cell; third longitudinal vein pro- 
vided with the usual peculiar stump in the 
subapical cell; a distinct cross-vein uniting 
