Form elongate oval. Labrum and mandibles produced beyond apex of clypeus. Antenna with 10 segments, antennal club with 3 tomentose segments. Anterior coxae transverse. Scutellum exposed. Metasternum longer than abdominal sternites. Metatibia with apical spines separated by basal metatarsal segment. Tarsal claws on all legs not independently movable, claws equal in length or size. Onychium not exposed beyond apex of fifth taromere, bisetose. Pygidium exposed beyond apices of elytra.

Classification Status
Arrow (1904) erected the subfamily Idiostominae for species that were previously placed in the genera Phyllognathus (Dynastinae), Oryctes (Dynastinae), and Orphnus (Orphninae). Arrow (1904) transferred species from these disparate groups into the genus Idiostoma Arrow. Because this name was preoccupied, Arrow (1940) proposed Allidiostoma as the replacement name for the genus and Allidiostomidae as the replacement name for the family (elevating the group from subfamily to family status). Lawrence and Newton (1995) amended the name to reflect the correct stem to Allidiostomatinae. No studies have commented on the relationships of this subfamily, although preliminary phylogenetic analysis based on molecular data indicates that the group is the sister taxon of the Orphninae (Ocampo et al in prep.).

This small subfamily includes one genus and 7 species. The group is resticted to southern South America. Allidiostomines superficially resembles members of the Dynastinae and some members of the subfamily were originally placed in such genera as Oryctes and Phyllognathus.

New World Genus of Allidiostomatinae
Allidiostoma Arrow 1940
Includes six species (Arrow 1912) that occur in Argentina, Chile, Peru, and Brazil.

Nothing is known of the ecology and biology of this small group of scarabs. Arrow (1904) reported that A. rufum (Arrow) possesses a stridulatory file on the inner face of the hind coxa.

Larvae. Larvae are not know for the group.

References Cited
ARROW, G. J. 1904. Sound-production in the lamellicorn beetles. Transactions of the Entomological Society of London 1904: 709-750.

ARROW, G. J. 1909. XV. On the characters and relationships of the less-known groups of Lamellicorn Coleoptera, with descriptions of new species of Hybosorinae, etc. Transactions of the Entomological Society of London 57: 479-507.

ARROW, G. J. 1912. Scarabaeidae: Pachypodinae, Pleocominae, Aclopinae, Glaphyrinae, Ochodaeinae, Orphninae, Idiostominae, Hybosorinae, Dynamopinae, Acanthocerinae, Troginae. Coleopterorum Catalogus pars 43, W. Junk, Berlin. 66 pp.

ARROW, G. J. 1940. A nomenclatural note (Coleopt.). Proceedings of the Entomological Society of London (B) 9(1): 16.

LAWRENCE, J. F. AND A. F. NEWTON, JR. 1995. Families and subfamilies of Coleoptera (with selected genera, notes, and references and data on family-group names), pp. 779-1006. In J. Pakaluk and S. A. Slipinski (eds.), Biology, Phylogeny, and Classification of Coleoptera. Papers Celebrating the 80th Birthday of Roy A. Crowson. Muzeum i Instytut Zoologii PAN, Warszawa, Poland.

RUIZ, F. 1924. El genero Idiostoma en Chile. Revista Chilena de Historia Natural 1924: 99-101.