Taxonomic revision of the Afrotropical scarab beetle genus Cerhomalus Quedenfeldt, 1884 (Coleoptera: Scarabaeidae: Orphninae)

The Afrotropical scarab beetle genus Cerhomalus Quedenfeldt, 1884 (Coleoptera: Scarabaeidae) is revised. Two new species are described: C. quedenfeldti sp. nov. and C. petrovitzi sp. nov. A new combination, Cerhomalus absconditus (Petrovitz, 1971) comb. nov., is established. The genus occurs in Central and West Africa with the majority of records from the Congo Basin. Keys, descriptions, illustrations of habitus and male genitalia, and distributional record map are given.


Introduction
The scarab beetles of the subfamily Orphninae Erichson, 1847, are a predominantly tropical group of insects distributed mostly in the southern continents. The Afrotropical Region is the centre of the diversity of orphnines, with over a hundred species occurring from Sahel in the north to Little Karoo in the south (Paulian 1948;Petrovitz 1971;Frolov 2005Frolov , 2013. Among the Afrotropical orphnines, there is a small group, Cerhomalus Quedenfeldt, 1884, which included two nominal species and was treated by different authors as either a distinct genus or a subgenus of Orphnus Macleay, 1819. Cerhomalus was erected by Quedenfeldt (1884) as a genus within the Orphninae (Orphnidae sensu Quedenfeldt) for a single species, C. mechowi Quedenfeldt, 1884, described in the same paper. In the diagnosis of the genus, Quedenfeldt (1884) mentioned the large size of the beetles (twice as large as specimens of Orphnus) and the clypeus with a transverse keel. After the original description, Cerhomalus was mentioned in a few papers including the catalogues by Arrow (1912) and Schmidt (1913). Paulian (1948) noted that the genus was more evolved than Orphnus but retained some ancestral characters; he did not discuss it in any detail, though. Petrovitz's (1971) work on the genus Orphnus was the only publication that included additional original information about Cerhomalus. He lowered the rank of Cerhomalus to a subgenus of Orphnus and described the second species of the genus, O. (C.) absconditus (Petrovitz 1971).
Cerhomalus has not attracted attention since Petrovitz (1971). In the course of our studies of the Afrotropical Orphninae, we have re-examined the material on Cerhomalus accumulated in all available collections to date and found that four distinct species of this group can be recognized. This necessitated examination of the types of the nominal species and a taxonomic revision of Cerhomalus. The aims of the present paper are to describe two species as new for science, provide a diagnostic key to all Cerhomalus species and illustrate their characters, as well as re-evaluate its subgeneric status suggested by Petrovitz (1971).

Material and methods
Morphological terminology follows . Preparation of specimens, digital images and locality map follow Frolov et al. (2017). Labels of the type specimens are cited verbatim with separate labels separated by a slash '/ʼ.

Differential diagnosis
Cerhomalus mechowi is most similar to C. petrovitzi sp. nov. but differs from it in having the widened part of a paramere (in lateral view) about half the length of the paramere (Fig. 1C, vs about ⅔ the length of the paramere in C. petrovitzi sp. nov. (Fig. 3D)) and the ventral fossa of a paramere shorter and wider (Fig. 1F, vs longer and narrower in C. petrovitzi sp. nov. (Fig. 3G)).

Type material
Lectotype (

Remarks
The male paralectotype housed in ZMHUB lacks the aedeagus.

Differential diagnosis
Cerhomalus absconditus can be easily separated from congeners by having the apices of the parameres rounded (in apical view), without semi-circular excavations (Fig. 2G, J) and without keels or fossae on ventral side (Fig. 2K), and the base of elytra with somewhat tile-shaped punctures ( Fig. 2A-B).   (Petrovitz, 1971).

Distribution
This is the most widely distributed species of the genus. The majority of records are from the Congo basin, but the species occurs up to Cameroon in the north (no precise locality is recorded) and to the Ancient Plateau in Angola in the south (Fig. 6).

Differential diagnosis
Cerhomalus petrovitzi sp. nov. is most similar to C. mechowi in having the ventral fossae on the apices of the parameres completely bordered (Figs 1F,3G) and the apices right angled in lateral view (Figs 1C,3D) but can be separated from it in having the widened part of a paramere (in lateral view) about two thirds the length of the paramere (Fig. 3D) and ventral fossa of a paramere longer and narrower (Fig. 3G).
Anterior margin of frontoclypeus somewhat rectangular, slightly convex in middle, bordered and slightly serrate in dorsal view (Fig. 3A). Frontoclypeus with a keel-shaped transverse process near anterior margin; height of keel about half its width. Surface of frontoclypeus almost smooth, with minute punctures. Eye tubercles feebly developed. Eyes rather large: width about 1/6 distance between eyes in dorsal view. Antennae 10-segmented.
Pronotum widely rounded laterally, as wide as elytra. Anterior border wide. Basal border narrow, keelshaped, separated from pronotal disc by deep groove with row of longitudinally elongated punctures. Pronotal disc with a rounded depression occupying more than half of the surface, somewhat rugose anteriorly. Most of pronotum surface covered with minute punctures separated by more than 3 puncture diameters. Anterolateral angles with much larger and denser punctures; posteriolateral angles with same punctures but in smaller numbers.
Scutellum subtriangular, narrowly rounded apically, about 1/10 length of elytra. Elytra 1.1 times longer than wide, with distinct humeral humps. Elytra widest in middle, lateral margins almost parallel in basal half. First (sutural) stria distinct, as groove with row of punctures. Other stria before humeral humps as rows of round setiferous punctures. Striae laterad of stria 5 feebly distinct. Elytral intervals covered with minute punctures, somewhat sparser than those on pronotum.
Aedeagus. Ventral fossae on the apices of the parameres completely bordered, long and narrow (Fig. 3G); apices of parameres right angled in lateral view, its widened part (in lateral view) about two thirds the length of paramere (Fig. 3D).

Female
Female (Fig. 3C) differs from male in having a relatively smaller, convex pronotum without tubercles and only with a small depression medially, frontoclypeus with much smaller, low keel not bimodal apically, protibial spur, and pygidium with rounded apex. Body length 21.0 mm.

Variation
Body length of examined male paratypes varies from 17.0 to 22.5 mm.

Distribution
The species is known from western Democratic Republic of the Congo (Fig. 6). The record from Nigeria is doubtful and need confirmation, therefore the specimen is not included in the type series.

Differential diagnosis
Cerhomalus quedenfeldti sp. nov. is similar to C. mechowi and C. petrovitzi sp. nov. in having the apices of the parameres with semi-circular excavations in apical view and with more or less developed fossae on ventral sides bordered with a keel, but can be separated from them in having the ventral fossae on the apices of the parameres not bordered proximally (Fig. 4G-K, arrowed) and the apices of the parameres in lateral view acute-angled (Fig. 4D, H).

Etymology
The new species is named after Friedrich Otto Gustav Quedenfeldt (1817-1891), a German coleopterist. Anterior margin of frontoclypeus somewhat rectangular, slightly convex in middle, bordered and slightly serrate in dorsal view (Fig. 4A). Frontoclypeus with a keel-shaped transverse process near anterior margin; height of keel about ⅔ its width. Surface of frontoclypeus almost smooth, with minute punctures. Eye tubercles feebly developed. Eyes rather large: width about 1/6 distance between eyes in dorsal view. Antennae 10-segmented.

REPUBLIC OF THE
Pronotum widely rounded laterally, as wide as elytra. Anterior border wide. Basal border narrow, keelshaped, separated from pronotal disc by deep groove with row of longitudinally elongated punctures. Pronotal disc depressed, somewhat rugose anteriorly. Most of pronotum surface covered with minute punctures separated by more than 3 puncture diameters. Anterolateral angles with much larger and denser punctures; posteriolateral angles with same punctures but in smaller numbers.
Scutellum subtriangular, narrowly rounded apically, about 1/10 length of elytra. Elytra 1.1 times longer than wide, with distinct humeral humps. Elytra widest in middle, lateral margins almost parallel in basal half. First (sutural) stria distinct, as groove with row of punctures. Other stria before humeral humps as rows of round setiferous punctures. Striae laterad of stria 5 feebly distinct. Elytral intervals covered with minute punctures, somewhat sparser than those on pronotum.

Female
Female (Fig. 4C) differs from male in having a relatively smaller, convex pronotum without tubercles, frontoclypeus with much smaller, low keel not bimodal apically, protibial spur, and pygidium with rounded apex.

Variation
Body length of examined male paratypes varies from 18.5 to 22.5 mm (males) and from 16.0 to 19.0 mm (females).

Distribution
The species is known from a few localities in the Republic of the Congo (Fig. 6).  (Petrovitz, 1971). B. C. mechowi Quedenfeldt, 1884. C. C. petrovitzi sp. nov. D. C. quedenfeldti sp. nov. Abbreviation: va. phlb. sc. = ventroapical phallobase sclerite. Not to scale. Petrovitz (1971) argued that Cerhomalus should be considered a subgenus of Orphnus based on the presence of the similarly shaped head and pronotum in different species of Orphnus. Indeed, the shape of the head and pronotum varies considerably within Orphnus and some species of this genus show the habitus similar to that of Cerhomalus. However, these are mostly the secondary sexual characters that are found in males and are subject to reasonable allometric variation. Phylogenetic value of such characters is unclear. Also, Petrovitz (1971) did not recognize the unique structure of the ventroapical part of the phallobase (see above), the character that distinguishes Cerhomalus from Orphnus. Therefore, until a phylogenetic analysis supporting the changes of the generic status of Cerhomalus is available, we follow Quedenfeldt and the majority of other authors and consider Cerhomalus as a separate genus.

Discussion
in the framework of the Russian State research project АААА-А19-119020690101-6 and partly supported by the Russian Foundation for Basic Research (grant 19-04-00565-A).