Hebecnema Confusion

I had been using the key in Fonseca's 1968 RES Handbook to identify a fly of the genus Hebecnema when I came across the following comments by Steven Falk and Howard Bentley in a 2008 thread at the DipteristsForum:

Steven Falk: ... Once you get to genus, remember that a couple of names in the old RES key (if this is what you are using) are now out of date i.e. vespertina (bare eyes, dark halteres) become nigra, affinis (bare eyes, yellow halteres) becomes vespertina. Also beware fumosa, males of which can have the tibiae so dark they almost seem black, and can take you to umbratica (though fumosa averages somewhat larger). ...

Howard Bentley: The difficulties of Hebecnema are compounded by errors in "The Muscidae of Central Europe" by Gregor et al. which many people are now using as their main key. You have to follow "Halteres with yellow knob" to get to vespertina, but the description of the species then gives the haltere colour as "dark brown to black". The latter is wrong. The only British Hebecnema with really black haltere knobs is nigra; in the key, "not black" would be a better description of haltere colour than "yellow" - they can be pretty dark in vespertina, but are certainly not black. Similarly, the key says that vespertina has "hind tibia usually with 2 anteroventrals", while the description says it usually has 1: in my experience the description is more often right here.

The authority for the affinis->vespertina; verspertina->nigra reassignment seems to be Pont, A.C. 1984. A revision of the Fanniidae and Muscidae (Diptera) described by Fallén. Entomologica Scandinavica 15, 277-297. I have not yet seen a copy of that paper, so to help me get things clear in my own mind, I constructed a copy of Fonseca's key interspersed with the comments of Falk and Bentley:

                   Genus Hebecnema Schnabl, 1889.

                             KEY TO SPECIES

1 (4) Legs largely reddish-yellow, or at least knees and extreme
      apices of femora conspicuously pale. Halteres yellow. Male: lower
      squama and its fringe distinctly brownish-yellow.

2 (3) All tibiae and middle and hind femora reddish-yellow. Abdomen
      tending to be somewhat translucent brownish and shining. Eyes
      practically bare. 5-6.75mm.

      Generally distributed. Frequent. ii-x...... 3. nigricolor Fallen.

3 (2) All femora mainly black, the extreme apex conspicuously pale in
      contrast to rest. Middle and hind tibiae usually obscurely
      translucent reddish.  Facial orbits in profile mainly (Male), or
      on lower part (Female), invisible. Male: eyes densely hairy;
      abdomen, seen from behind, rather densely dusted brownish-grey
      with a hardly discernible median darker area. Female: eyes
      microscopically but distinctly pubescent; frontal triangle, seen
      from slightly behind, not extending more than halfway from front
      ocellus to lunule. 5.5-6.25 mm.

      Worcs., Middx., Gloucs., Berks., Oxon., Somerset, Hants., Devon
      and Surrey. Uncommon. iii-x.................... 2. fumosa Meigen.

4 (1) Legs entirely black or brownish-black, at most the knees
      occasionally obscurely reddish. Facial orbits, in profile, quite
      distinct throughout their length. Male: lower squama whitish
      with pale yellow fringe.

5 (6) Eyes densely long. (Male) or short- (Female) haired. Abdomen,
      seen from behind, with (Male) rather dense grey dusting and a
      sharply defined narrow median dark line, or (Female) with thin
      dusting and a broader, less sharply defined dark median area and
      faint shifting dark spots. Female: thorax, seen from in front,
      with 4 faint but more or less distinct darker stripes; frontal
      triangle, seen from slightly behind, usually extending almost to
      lunule.  3.5-6mm.

      Generally distributed. Very common. iv-x.... 1. umbratica Meigen.

        Falk: Also beware fumosa, males of which can have the tibiae
        so dark they almost seem black, and can take you to umbratica
        (though fumosa averages somewhat larger).

6 (5) Eyes practically bare. Thorax and abdomen more uniformly dull
      brownish. black, without distinct markings.

7 (8) Halteres with brownish-black to black knob and paler stem. Hind
      tibia.  with only 1 anteroventral bristle. 4-5.25 mm.

      Scotland: Morays., Inverness. and Aberdeens. England and Wales:
      Norfolk, Herefords., Glamorgan. Gloucs., Berks., Oxon., Herts.,
      Somerset, Hants., Devon and Kent. Fairly common.
      iv-ix...................................... 4. vespertina Fallen.

        Falk: vespertina (bare eyes, dark halteres) become nigra

8 (7) Halteres entirely yellow. Hind tibia with 2 anteroventrals.
      4-5.5 mm.

      Generally distributed. Common. v-x........... 5. affinis Malloch.

        Falk: affinis (bare eyes, yellow halteres) becomes vespertina.

        Bentley: the key [of Gregor et al] says that vespertina has
        "hind tibia usually with 2 anteroventrals", while the
        description says it usually has 1: in my experience the
        description is more often right here.

So my fly, which in Fonseca keys out to affinis but has only 1 anteroventral, is probably what is now known as vespertina.