Key to Subgenera of Ambrysus and Species of the Subgenus Syncollus of Mexico

Identification of species of Syncollus relies heavily on the condition of the male accessory genitalic process of tergum VI (AGP) and the female mediosternite VII (subgenital plate or SGP). As such, the abbreviations AGP and SGP are used throughout the following key and in the Annotated List of Species.

1. Male and female with mesal extensions of propleura closely appressed to posterior part of prosternum (prosternellum), thus propleura and anterior part of prosternum (probasisternum) at same level (Fig. 1 A). Male abdominal tergum V expanded posteriorly to cover abdominal segments VI–VIII (Fig. 2 A)............................ Ambrysus (Syncollus) La Rivers ...2

1'. Male and female with mesal extensions of propleura detached from prosternellum, thus propleural extensions further ventrad than probasisternum (Fig. 1 B). Male abdominal tergum V slightly expanded posteriorly, with central notch, covering only basal part of terminal abdominal segments (Fig. 2 B)...................................... Ambrysus (Ambrysus) Stål

2. Male and female with minute discontinuous tubercles and punctures on hemelytra. Male posterolateral corner of laterotergite V obtuse and not spinose; AGP short, curved to right at 45 degree angle, pointed distally (Fig. 12 B); medial lobes of tergum VIII (pseudoparameres) long, asymmetrical, with left pseudoparamere slightly longer and narrower (Fig. 12 C). Female with posterior margin of SGP broadly excavated with concavity twice as wide as deep, bounded by posterolateral corners (Fig. 12 F)................................................................................. .. Ambrysus xico n. sp.

2'. Male and female with tubercles on hemelytra interconnected by continuous sclerotized ridges, giving a polygonal appearance surrounding punctures. Male posterolateral corner of laterotergite V acute; AGP long or short, curved to right at ≥ 45 degrees,

rounded distally; pseudoparameres long or short, generally symmetrical. Female with posterior margin of SGP not as above, but if central concavity twice as wide as deep then body length ≤ 6.8 mm or concavity occupies only 1/3 of posterior margin (Fig. 5 F)............................................................................................ 3 3. Male with AGP long, narrow, parallel-sided, not dilated or pointed distally (Fig. 7 B); pseudoparameres long, rounded, asymmetrical, with right pseudoparamere slightly narrower at apex (Fig. 7 C). Female with posterior margin of SGP highly variable (see variation section) but generally with a shallow concavity bearing a central notched lobe (Fig. 7 F)........................................................................................... Ambrysus circumcinctus Montandon

3'. Male with AGP short, dilated distally; pseudoparameres generally short and symmetrical, but if long then pseudoparameres asymmetrical, with left pseudoparamere narrower transversely (Fig. 9 C). Female with posterior margin of SGP straight and bearing a small central concavity (Fig. 5 F), or narrow with an inverted V-shaped notch (Fig. 9 F), or large concavity twice as wide as deep (Fig. 3 F), or shallow concavity with two central pointed lobes (Fig. 10 F).............................. 4

4. Male with AGP curved to right at approximately 45 degree angle, mesal margin evenly curved (Fig. 9 B); pseudoparameres asymmetrical, with left pseudoparamere slightly narrower transversely and longer than right (Fig. 9 C). Female with SGP narrowed subapically (bottleneck-shape), posterior margin with inverted V-shaped notch (Fig. 9 F)..................................................................................................... Ambrysus pygmaeus La Rivers

4'. Male with AGP curved to right at ≥ 45 degree angle, if 45 degrees then mesal margin roundedly angulate (Fig. 10 B); pseudoparameres almost symmetrical (Figs. 3 C, 5C, 10C). Female with posterior margin of SGP straight and bearing a small central concavity (Fig. 5 F), or large concavity twice as wide as deep (Fig. 3 F), or shallow concavity with two central pointed lobes (Fig. 10 F)............................................................................................ 5

5. Male with AGP curved to right at nearly 90 degree angle (Fig. 3 B); pseudoparameres with posterior margin straight (Fig. 3 C). Female with posterior margin of SGP with large central concavity almost twice as wide as deep (Fig. 3 F)..................................................................................... Ambrysus baeus Polhemus & Polhemus

5'. Male with AGP curved to right at ≤ 60 degree angle; pseudoparameres with posterior margin straight (Fig. 10 C) or slightly convex (Fig. 5 C). Female with posterior margin of SGP straight and bearing a small central concavity (Fig. 5 F) or shallow concavity with two central pointed lobes (Fig. 10 F)............................................................. 6

6. Male with AGP curved to right at nearly 60 degree angle (Fig. 5 B); pseudoparameres with posterolateral corners roundedly angled ~45 degrees (Fig. 5 C). Female with posterior margin of SGP straight bearing a small central concavity (Fig. 5 F).................................................................................. Ambrysus chiapanecus n. sp.

6'. Male with AGP curved to right at nearly 45 degree angle (Fig. 10 B); pseudoparameres with posterolateral corners narrowly angled nearly 90 degrees (Fig. 10 C). Female with posterior margin of SGP with shallow concavity with two central pointed lobes (Fig. 10 F).................................................................. Ambrysus totonacus n. sp.