Dixa vockerothi sp. nov. (Figs 18–20, 23) Dixa brevis Peters & Cook, 1966: 241, not Garrett, 1924: 6 (misidentification of northeastern North American specimens). Type material. HOLOTYPE, ♂ labeled: “Old Chelsea/ Que. 5.xi.1958 / J.R. Vockeroth”; “ Dixa brevis / Garrett/ Det. T.M. Peters 1964”; “HOLOTYPE/ Dixa / vockerothi / J.K. Moulton [red label]” (CNC). PARATYPES: Old Chelsea, 5.xi.1958, J.R. Vockeroth (10♂; CNC); Same data, except 15.x.1958, J.R. Vockeroth (10♂; CNC). Additional material examined. CANADA: NS: Grande Anse R, Cape Breton Highlands NP, 8–10.vii.1984, I.M. Smith (1♂, CNC); Kentville, 6.viii.1958, J.R. Vockeroth (14♂; CNC); Lone Shieling, swept along fast rocky stream, 11.vii.1983, J.R. Vockeroth (2♂, 2♀; CNC). ON: Normandale, 42°42′ 80°19′, 21.v.1956, J.R. Vockeroth (1♂, CNC); Sterling, 14.x.1956, J.R. Vockeroth (2♂, CNC); Ottawa, 30.ix.1956, J.R. Vockeroth (1♂, CNC); Ottawa, Hog ′s Back, 16.x.1947, G.E. Shewell (2♂, CNC). QC: Eardley, 18.x.1956, J.R. Vockeroth (2♂, CNC); Gatineau Park, Mackenzie King Falls @ Waterfall Tr, N45°28′41.08″ W75°51′02.98″, ex. above falls, 24.vi.2009, B.J. Sinclair (2♀, CNC); King Mtn, sm str, 16.xi.2011, B.J. Sinclair (1♂, CNC); Lac Philippe [Gatineau Park], 45° 37′N 76°W, 22.viii.1959, J.R. Vockeroth (1♂, CNC); Old Chelsea, Mulvihill Brook at Mountain Rd, in one moderately dense swarm 6–8′ over stream, 5.xi.1958, J.R. Vockeroth (22♂, 1♀, CNC: ethanol); Old Chelsea, 5.xi.1958, J.R. Vockeroth (21♂, CNC); Old Chelsea, 15.x.1958, J.R. Vockeroth (42♂, CNC); Old Chelsea, 5.ix.1958, C.H. Mann (1♂, CNC); Old Chelsea, 22.vii.1956, J.R. Vockeroth (1♂, CNC); Mt. Orford, 29.viii., 9.ix.1937, G.E. Shewell (2♂, CNC). USA: NC: HAYWOOD COUNTY, Woodfin Cascade, Blue Ridge Parkway NP, N35°27′08.30″ W83°06′10.6″, 16.vii.2006, J.K. Moulton & G.R. Curler (2♂, 1L, ANSP); same locality, 24.vii.2011, JKM (1♀, ANSP). NY: CATTARAUGUS COUNTY, Stoddard Hollow, 1720–1880 ft, 42°4′N W78°45′, 10.viii.1961, D.L. Deonier / J.L. Laffoon (10♂, 2♀, ISIC). Diagnosis. This species can be distinguished from D. ubiquita sp. nov. and D. elkmontensis sp. nov. by the following characters: Morphological. Basal gonocoxal lobe with apex more digitiform and dorsally directed (Fig. 18 vs. 12, 15), creating more conspicuously concave horizontal margin, most noticeable in terminal view (Fig. 20 vs. 14, 17). Anterior lobe of SES acute apically, with thin, strap-like, connection to ventral apodeme of proctiger acutely angled; distal lobe of SES narrow, lip-like in lateral view (Fig. 18). Apex of gonostylus not strongly twisted ca. 90° medially, most obvious in ventral view (Fig. 19). Molecular. Within the 66 nucleotides (22 codons) shown (Fig. 35) a thymine at position 46 (vs cytosine), an adenine at position 51 (vs. guanine), and a guanine at position 54 (vs. cytosine) serve to distinguish this species from the other two. Within the encompassing amplified fragment of BZF, D. vockerothi sp. nov. is 6.1% divergent from D. ubiquita sp. nov. and 9.1% divergent from D. elkmontensis sp. nov. (JK Moulton, unpublished). Description. Male. Same as D. ubiquita sp. nov., except as follows: Wing length (n =10) 3.8–4.1 (avg=4.0) mm. Terminalia (Figs 18–20): Basal gonocoxal lobe narrowed, less than half as broad as gonocoxite depth, with apex more digitiform and dorsally directed, with ventral margin straight to slightly convex (Fig. 18). Gonostylus with apex straight, not twisted ca. 90° medially, most obvious in ventral view (Fig. 19). Anterior lobe of SES rounded apically, with connection to 9T and ventral apodeme of proctiger broader; distal lobe of SES narrow, liplike in lateral view (Fig. 18). Female. Wing length (n =7) 4.4–4.9 (avg=4.6) mm. Not reliably distinguishable from D. ubiquita sp. nov. or D. elkmontensis sp. nov. Etymology. Named in honor of Dr. Richard (Dick) Vockeroth, who collected numerous adults of this species, including the type series, from several localities in and around the Gatineau area and elsewhere in eastern Canada. Distribution. Dixa vockerothi sp. nov. appears to be the most northerly distributed of the three members of this species group (Fig. 34). It is confirmed from numerous localities in the Gatineau Hills region of Quebec, a few sites in Nova Scotia, one site in the Alleghany Mountains of Pennsylvania, and one site in the Southern Appalachian Highlands of western North Carolina. Remarks. Dixa vockerothi is found in high gradient, rapidly flowing streams 3–5 m in width with waterfalls, often stair-cased ones (Figs 32, 33). It occurs with D. ubiquita sp. nov. in Woodfin Cascades in western NC, and no other dixid associations are known.

Published as part of Moulton, John K., 2017, The true identity of Dixa modesta Johannsen (Diptera: Dixidae) resolved: synonymy of Dixa similis Johannsen, designation of the Dixa ubiquita species group, and description of three new eastern Nearctic species, pp. 247-260 in Zootaxa 4216 (3) on pages 256-258, DOI: 10.5281/zenodo.231794