Holotype male, dissected, labeled: a) “male symbol label”; b) “Brasil, Amazonas, Uarini, / 03°02'57"S, 65°41'42"W, / 22/VII-03/VIII/1995, P./ Bührnhein, N.Aguiar & al.”; c) handwritten label “NO ALBURNO DE/ TRONCO CAÍDO/ 01/VIII/1995” (UFAM).

Paratypes, 4 males and 7 females labeled: 1 female a) “female symbol label”, b) “Brasil, Amazonas, Uarini, / 03°02'57"S, 65°41'42"W, / 22/VII-03/VIII/1995, P./ Bührnhein, N.Aguiar & al.”; c) handwritten label “NO ALBURNO DE/ TRONCO CAÍDO/ 01/VIII/1995” (CEMT). 3 females labeled “Brasil, Amazonas, Coari, / Duto Urucu/Porto Terminal, / 04°50'16"S, 65°20'36"W, / 16/VI/1996, Buhmheim (sic), / PF, Aguiar, NO, Arruda, / AMR & Gualberto, TL col.” (UFAM). 1 male labeled a) “Brasil, Amazonas, Coari, / Duto Urucu/Porto Terminal, / 04°50'16"S, 65°20'36"W, / 16/VI/1996, Bühmheim (sic), / P.F. & Aguiar, N.O. col.”; b) handwritten label “Em tronco/ caído” (EPGC). 1 female labeled “PERU, Junin, Puerto/ Ocopa, I-2007, 600m/ 11°07'50"S, 74°17'46"W/ S.Castro col.” (EPGC). 1 female a) “BRASIL: Rondônia: Porto/ Velho, margem direita/ do Rio Madeira, IX-2004” (EPCG). 1 male labeled “PERU, Ucayali, Via/ Puerto Ocopa-Ucayali, / XII-2009, 1200m, / 11°03'51"S, 74°15'39"W/ S. Castro col.” (MIIS); 1 male labeled “PERU, Junin, Huerto/ Eden c.a, near Puerto/ Prado XII-2009/ 1800m, local collector” (JSC). 1 male labeled a) “BR 14, Km 92/ Pará, Brasil/ E. Lobato XII. 60” (IOC). 1 female labeled a) handwritten label “S. Paulo de/ Olivença/ Solimões/ VIII. – Fassl”, b) “Coleção/ J. F. Zikan” (IOC). All paratypes additionally labeled, yellow label, “Amblyodus castroi/ PARATYPE/ Grossi & Grossi.

Head with frontal horns less divergent, being almost parallel (Fig 3). Pronotal disc more declivous than in Amblyodus taurus with lateral carinae distinctly higher in males majors (Fig 4), posterior furrow deeply excavated as opposed to a less excavated furrow in Amblyodus taurus (Figs 9 and 10). Aedeagus with internal margin of parameres concave, not parallel; external margin less constricted than in Amblyodus taurus where internal margin is almost parallel, and external margin abruptly constricted (Figs 11 and 12).

(Figs 1 and 2). Total body length 20 mm. Total pronotal width 9.2 mm. Body elongated, about 2 times longer than wide, color dark brown dorsally and reddish brown ventrally; dorsal surface glabrous, with sterna being setose. Head: Surface smooth and glabrous with sparse micropunctures; in frontal view with two lateral, concave areas with scattered C-shaped puntures. Clypeus subtriangular, laterally bordered and slightly upturned, convex and with acute apex. Canthi intruding upon eyes just before first third. Frons with two erect, diverging, posteriorly recurving horns. Interocular width equals 3.3 mm. Mandibles tridentate with inner tooth more acute; teeth upturned. Antennae 10 segmented with scape as long as the 6 next segments; club with segments subequal in length. Pronotum: Shape trapezoidal, narrower than both elytra together; discal area with C-shaped punctures combined with reticulated areas, flat and declivous; anterior border incomplete. Lateral and posterior sides of pronotal depression strongly carinated, anterior carina more pronounced, higher, being convex and wider posteriorly; carina at base weakly emarginate; carina posteriorly interrupted at middle by a longitudinal furrow, internally weakly angulate; furrow about 4.5 times narrower than head width. Anterior angles acute, posterior angles rounded. Outer side and lateral posterior side of pronotal surface punctate; punctures ocellate, sometimes coalescent, posteriorly larger. Elytra: Discal area with 5 rows of large ocellate punctures, rows weakly impressed. Interstriae slightly convex, with scattered small punctures. Lateral edges with 5 similar rows of ocellate punctures, instead of by some ocellate punctures between third and fourth rows. Pygidium: Shape convex in lateral view; surface densely punctate; punctures ocellate, moderately sized, elongate near dorsal margin. Sixth ventrite sinuous at middle. Legs: Protibiae quadridentate, proximal tooth smaller, distal ones bigger. Metatibiae with 5 apical teeth. Parameres: Shape symmetrical, narrower at apex; apex dilated, laterally roundly angulated, apically rounded, triangle shaped; internal side of each paramera concave, not parallel (Fig 5). In lateral view shaft constricted, with a post-anterior concavity; dorso-ventral carina incomplete, not reaching ventral margin; with a flat, truncate tooth near base (Fig 6).

Female paratypes. Similar to male in general aspects except for the following characters: Head: Frontal horns less developed and never reaching pronotal middle. Pronotum: Pronotal depression narrower, near anterior margin smooth, not punctate; lateral carina smaller with a weak acute projection before first third (Figs 7 and 8); pronotal furrow longer, ending just before posterior margin. Pygidium: Shape wider laterally and shorter, with punctures smaller. Sixth ventrite not sinuous at middle.

Smaller males possess less developed and less posteriorly recurving frontal horns. Pronotal carina very weakly pronounced (Figs 13 and 14).

The species is named castroi in homage of Sergio Castro who provided us with part of the paratypes from Peru.

When recording the new occurrence of Amblyodus taurus for South America, Gasca and Aguiar (2008) misapplied the name Amblyodus taurus to the material they had on hand. Actually both species of Amblyodus are similar in appearance, which is common in Phileurini. The authors also stated that the only two genera of the tribe that possess elongate frontal horns were Amblyodus and Oryctophileurus Kolbe, 1910. However, Ceratophileurus Ohaus, 1911 also possess this character in both sexes (Gillett et al. 2010).

Amblyodus and Oryctophileurus share the lateral pronotal carina and pronotal shape: elongate, widely flattened, depressed with discal depression totally wrinkled. Additionally, both genera have almost no external sexual dimorphism, as females also possess a well-developed frontal horn, a feature that makes the distinction between genders difficult, being the shape of the last sternite the better way to determine gender in these cases. Moreover parameres have almost the same shape, and the shape of prosternal process is also shared between Amblyodus and Oryctophileurus, namely flat ventrally and with a spine-like process posteriorly. Based on several morphological characters, there is a possibility that Oryctophileurus could be a synonym of Amblyodus because the unique feature to distinguishing both genera is the number of frontal horns, one or two, which is not a good character within Dynastinae as some genera are usually extremely allometric. Only with the examination of the type species of Oryctophileurus, will it be possible to affirm if they are congeneric or not.

The holotype male is an incomplete specimen and it was apparently damaged by an axe during collecting inside dead logs. It is the same male specimen illustrated by Gasca and Aguiar (2008, figure 1, male in lateral view).

The genus Amblyodus is recorded for the first time from Peru and from Brazil states of Pará and Rondônia (Fig 15). It is possible that Amblyodus castroi occurs in all the Amazonian subregion.

Characters used to diagnose the genus by Ratcliffe (2003) and Ratcliffe and Cave (2006) are confirmed with the new species described here, except for the presence of six teeth on the apex of the metatibiae. In Amblyodus castroi, that is a variable character, as the number of teeth may be five or six.