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Type species: Bolboceras tubericeps Fairmaire, 1861 by original designation.

Description. Form (Figs. 1-37): Color usually reddish-brown to black, the lighter brown coloration of some specimens is likely the incomplete scleritization of newly emerged adults (teneral coloration); body spherical, strongly convex. Size moderate (length 7.5-22.0 mm; width 4.0-10.0 mm). Head in male: Subtriangular or trapezoidal, longer than wide. Mandible with outer margin rounded, weakly sinuate or almost straight, anteriorly with apex acute, curved inwards. Labrumwithapex variably emarginated; dorsal surface rugose or rugopunctate. Clypeus and frons with variable ornamentation (Figs. 1-37). Some species have cephalic armature that is either comprised of 1 horn at midline of clypeal apex or of 2 horns. In the case of 2 cephalic horns, 1 is at midline of clypeal apex and the other horn (depending of the species) is either located on the clypeus immediately behind the first or further back at the frontoclypeal margin or between the eyes. Another type of armature consists of a large anteriorly directed clypeal horn and 2 large horns that originate in the ocular margin. In some cases, the cephalic armature either consists of 1 anteriorly directed clypeal horn and 4-5 small horns situated behind the clypeal horn in different places on the head or with a prominent trapezoidal frontal tubercle formed by 4 tubercles joined laterally by a longitudinal carina. Frons impunctate to sparsely puncture, finely rugose. Vertex dorsally smooth, only with micropunctures, flat or depressed. Antenna with 11 antennomeres; antennomere 1 shorter than 2-8 combined. Antennal club ovoid, with 3 antennomeres (Fig. 47); outer antennomere usually more convex than the inner antennomere; dorsal surface completely setose; basal antennomere weakly convex, often nearly flat; dorsal surface partially setose on outer distal margin. Eyes partially divided by canthus; eye canthus with outer lateral margin arcuate or straight, surface generally rugopunctate. Pronotum: Sexually dimorphic, males generally with deeper anteromedian excavations. Pronotum transverse, convex, without horns, generally with deep and wide anteromedian excavation (except in B. tricorne); dorsally either with posterior transverse ridge parallel to basal margin (not always present in Bolborhinum) or with a pair of prominent protuberances in the anterior margin of the pronotum and with the lateral border projected anteriorly (B. trilobulicorne). Dorsal surface sparsely punctate, sometimes with impressed medial furrow; lateral surface with moderately dense to dense punctation concentrated around the lateral fovea, on the anterior and posterior angle of pronotum, and along the lateral margin. Scutellum: Triangular, length less than basal width (Fig. 50); surface with punctures small, variable in density; lateral margin curving inward at base; basal margin slightly arcuate or straight; apex of scutellum subacute or rounded. Elytron: Convex; anterior margin not upturned; surface with 7 variably impressed striae between suture and humeral umbone; puncture small to moderate, separated by 1 or more puncture diameters; intervals smooth, only with micropunctures; second stria almost reaching elytral base. Venter: Surface with setation yellowish-brown or tawny brown, long, moderately dense, partially covering thorax and abdomen; abdominal sternites densely punctate. Prosternum posteriorly with apical tooth, dorsally with median carina. Mesocoxae subcontiguous. Metasternum pyriform, bulbous, convex medially, with median long metasternal carina; dorsally with small, dense punctures, partially covered by moderately dense, long setae; metasternal process anteriorly truncate. Legs: Protibia with 5 to 6 teeth on outer margin; teeth with acute or rounded apex; protibial spur subparallel, straight, acuminate at apex, length equals or exceeds the apex of the second protarsomere. Protarsus with first tarsomere longer than fifth, second to fourth tarsomeres decreasing in length. Mesotibiae and metatibiae robust, variable shaped in lateral view, but always with unlobed subapical carina and with knob-like projections randomly spread over surface above subapical carina. Male genitalia: Symmetrical, weakly scleritized; aedeagus small, simple in structure, subparallel-sided; parameres short, basally membranous, with apex narrow distally, obtuse (Fig. 53).
Female. As male except in the following respects. Head: trapezoidal; shorter than in the male; dorsally without horns, but with a variably developed tubercle or tubercles on frontoclypeal region or frons; with a pair of short lateral carinae that converge distally. Clypeus truncate and elevated apically, dorsally rugulose. Pronotum: without anteromedian excavation, only with small concavity or depression located immediately behind of the apical margin of the pronotum. Female genitalia: not diagnostic.

Species: (click on species names for information)
Bolborhinum geotrupoides (Laporte, 1840)
Bolboceras geotrupoides Laporte, 1840: 104 (original combination)
Bolboceras binasutum Fairmaire and Germain, 1861: 2 (junior synonym)
Bolboceras distinguendum Fairmaire and Germain, 1861: 2 (junior synonym)
Distribution: Chile, Región Metropolitana de Santiago to XIV Región de Los Ríos; Argentina, Provinces of Neuquén and Río Negro.

Bolborhinum laesicolle (Fairmaire, 1856)
Bolboceras laesicolle Fairmaire, 1856: 483 (original combination)
Bolboceras excavatum Philippi, 1859: 660 (junior synonym)
Bolboceras mundum Redtenbacher, 1868: 60 (junior synonym)
Distribution: Chile, VIII Región del Biobío to X Región de Los Lagos; Argentina, Provinces of Neuquén and Río Negro.

Bolborhinum nasutum (Fairmaire and Germain, 1861)
Bolboceras nasutum Fairmaire and Germain, 1861: 2 (original combination)
Bolboceras andicola Philippi, 1873: 312 (junior synonym)
Distribution: Chile, V Región de Valparaíso to VIII Región del Biobío.

Bolborhinum seai (Martínez, 1951)
Bolboceras seai Martínez, 1951: 113 (original combination)
Distribution: Argentina, Province of Catamarca.

Bolborhinum shajovskoyi (Martínez, 1952)
Bolboceras shajovskoyi Martínez, 1952: 318 (original combination)
Distribution: Chile, IX Región de La Araucanía; Argentina, Provinces of Mendoza, Neuquén, and Río Negro.

Bolborhinum tricorne (Solier, 1851)
Bolboceras tricorne Solier, 1851: 67 (original combination)
Distribution: Chile, IV Región de Coquimbo to VIII Región del Biobío.

Bolborhinum trilobulicorne Mondaca and Smith, 2008
Distribution: Chile, VII Región del Maule.

Bolborhinum tubericeps  (Fairmaire, 1856)
Bolboceras tubericeps Fairmaire, 1856: 483 (original combination)
Bolboceras bicorne Philippi, 1859: 659 (junior synonym)
Bolboceras tetraodon Redtenbacher, 1868: 59 (junior synonym)
Distribution: Chile, VII Región del Maule to IX Región de La Araucanía.