This image (full-size version here
) includes an inset of Fig. 62 from pg. 730 of the Manual of Nearctic Diptera(1)
, which is meant to illustrate the following couplet in the key to the genera of Syrphidae on pg. 718 of the MND(1)
3a) Lower lobe of calypter with many long coarse yellow hairs above, especially on posteromedial portion (Fig. 62)....Syrphus Fabricius3b) Lower lobe of calypter with only microscopic pile above or, rarely, with a few very fine pale scattered erect hairs........4 (key continues)
In the MND figure (see inset), the plane of the calypters and the plane of the wing blade roughly coincide...as would be the case in a well-prepared pinned specimen with its wings extended fully-forward. But in my photo, the wings are not
extended fully-forward, and I interpreted the plane of the calypters (illustrated in "transverse view" in Fig. 62) as being "folded downward" by about 60° so that the upper & lower calypters are oriented in a steeply oblique plane relative to the horizontal position of the wing blade. With that interpretation, I can barely make out many long yellow hairs which seem in accord with what's written in lead 3a) above.
However, after being prompted to look further into the "calypter hairs" character by Bill Dean's comments under the 1st image in this series, I found the equivalent key break illustrated rather differently with this image
in the 2013 CJAI Key to Neartic Syrphidae
To my eye, the depictions of the "lower calypter hairs character" in Fig. 62 of the MND and the CJAI link
are quite different looking. Without further clarification I wouldn't be able to tell whether they both accurately show different variations within a spectrum of how this character is manifested...or if (as Bill Dean's comments seem to indicate) the wording and figure in the MND misled me, and the character is always manifested in the manner shown in the CJAI link
. (These sorts of details can be irksome, since often one must learn morphology and taxonomy from reading the literature...and typically cognoscenti are not at hand to tutor one in the seemingly "unwritten folklore" of how various technical characters are interpreted in practice.)
For (many!) more details on ID issues for this post, see the remarks and comments under the 1st and 4th images of the series.