4 
i 
Fe 
culiciformis, De Geer. 379 
As early as the year 1831, Ruthe, in “ Einige Bemerkun- 
gen und Nachtriige zu Meigen’s ‘ Systematische Beschreibung 
der europiiischen Zweifliigeligen Insekten,’” (‘ Isis,’ 1831, 
pp. 1203-22), described a new gnat under the name of 
Corethra velutina, which he stated to be very nearly allied 
to C. culiciformis, Meig. (or rather De G.), but whick, besides 
the colour and clothing, could be easily distinguished by the 
proportions of the tarsal joints, and by the structure of the 
last joint and the claws. He seems to have captured only a 
single male. Among the characters of the new species the 
particular statement of the very short first tarsal joint could 
not but strike so distinguished a dipterologist as Loew * ; and 
in his ‘ Beschreibungen einiger neuen Gattungen der euro- 
piischen Dipterenfauna”’ (Hut. Zeit. Jahrg. v., 1844) he 
took occasion to establish, for Ruthe’s Corethra velutina, a 
new genus, Mochlonyx, which he characterized (/. c. p. 121, 
note) as follows :— Mochlonyx, M., a genus coming next to 
Corethra, which, among other things, is very easily distin- 
guished from the latter by its first tarsal joint being very short, 
namely, one fourth the length of the second, the fifth of the 
same structure as in Lponewra, and the claws bifid at the 
apex, and furnished at the base with a downwardly directed 
process (vid. tab. 1. fig. 11).” The figure cited gives a 
rather rough representation of the last tarsal joint with the 
claws. ‘The character of Mochlonyx here given may cer- 
tainly be regarded as stating the chief differences as compared 
with the nearly allied genus Corethra ; but besides that it is 
too scanty, and therefore insufficient to give a zoological image 
of the new generic form, it has the further great imperfection 
that it is made solely from the male, and that the character 
taken from the structure of the last claw-jomt with the claws, 
which alone are figured, does not apply to the female, which 
has far simpler claw-joits and claws. For in this genus we 
find the unusual case that the sexes differ not only in the 
usual way in the structure of the antennae, head (including 
the mouth parts), and the generative organs, but that also the 
claw-joints and the claws differ according to the sex. 
bears one of the best-known of zoological names, and the larva of which 
has acquired a classical reputation as the object of histological investiga- 
tions. If sucha change is eventually to be made, it had better remain over 
for some future monograph of this group. [See also note p. 875.—W.S. D. | 
* Zetterstedt, who also, in his third supplement, has Ruthe’s species, 
Corethra velutina, from Oland, makes no remark upon this character, but 
seems not to have been acquainted with Loew’s article here cited, al- 
though it had appeared eleven years before. 
28* 
