Key to Cavonus males (modified from Carne 1957)

1. Clypeus with sides sinuate (Carne 1957, Fig. 334); elytra with dorsal striae obsolete posterior to subapical calli; basal pronotal ridge continuous...................................................................................... 2

- Clypeus rounded (Carne 1957, Figs. 343, 351); elytra with dorsal striae continuing over subapical calli; basal pronotal ridge sometimes partially obsolete............................................................................ 3

2. Pronotum armed with lateral horns (Carne 1957, Fig. 339); frons without a transverse excavation behind clypeofrontal ridge (Carne 1957, Fig. 334); pronotal impression continuous to basal margin; genitalia as in Carne (1957, Figs. 341, 353); body 14–22 mm long; southern South Australia ................................................ C. armatus Sharp, 1875

- Pronotum with lateral convex elevations, frons with a transverse excavation behind clypeofrontal ridge (Carne 1957, Fig. 340); basal convexity of pronotum interrupted by a shallow depression extending to basal margin; genitalia as in Carne (1957, Figs. 342, 350); body 12–21 mm long; southern South Australia ................................. C. sharpi Blackburn, 1888

3. Apical pygidial ridge glabrous........................................................................... 4

- Apical pygidial ridge setose............................................................................. 5

4. Pronotum with lateral horns; mentum highly compressed; body about 12 mm long; southwestern South Australia ........................................................................................... C. acutifrons Lea, 1917

- Pronotum with lateral convex elevations; mentum very conspicuous, depressed, strongly reflexed at ligula; body 15–17 mm long; southeastern South Australia, northwestern Victoria ................................ C. niger (Blackburn, 1888) .

5. Pronotum with a pair of anteromedian tubercles (Carne 1957, Fig. 351), with strong convexity at base and with basal ridge either continuous or obsolete; scutellum punctate or rugose on disc; genitalia as in Carne (1957, Figs. 344, 347); body 11–12.5 mm long; southeastern South Australia, northwestern Victoria ............................ C. bidens (Blackburn, 1896)

- Pronotum with single anteromedian tubercle; disc of scutellum either coarsely punctate or bearing submarginal garland of small punctures (Carne 1957, Fig. 353); genitalia unknown or as Figs. 9–10 or Carne (1957, Figs. 345, 349).................. 6

6. Pronotum with small elevated tubercle (Carne 1957, Fig. 348); basal ridge obsolete in lateral thirds, sometimes discernible on median third; elytral punctation moderately impressed, dorsal stria obsolete just before apical calli; southwestern New South Wales ................................................................................ C. leai Carne, 1957

- Pronotum with short, stout, erect anteromedian tubercle (Carne 1957, Fig. 338); basal ridge continuous; elytral punctation deeply impressed, dorsal striae not obsolete at subapical calli; southwestern South Australia and southern Western Australia .. ................................................................................................... 7

7. Apical palpomere of mandibular palp cylindrical; pronotal impression with medial elevation (Figs. 3, 6); clypeal surface (Fig. 7) heavily punctate; scutellum (Fig. 3) with submarginal garland of punctures; genitalia as in Carne (1957, Figs. 345, 349); body 18–19 mm long; southwestern South Australia, southeastern Western Australia (Fig. 28)................................................................................................... C. sculpturatus Blackburn, 1888

- Apical palpomere of mandibular palp conical, widest and truncate at apex; pronotal impression uniformly concave (Figs. 17, 20); clypeal surface (Fig. 21) with fine sparse punctures; scutellum (Fig. 17) disc coarsely punctate; genitalia as in Figs. 23–24; body 15.5 mm long; southwestern Western Australia (Fig. 28)........... C. fovealacus Hutchinson & Allsopp, new species