The Diphyllostomatidae includes three species in the genus Diphyllostoma. The group is endemic to the west coast of California in the United States. The natural history of the group is poorly known, and larvae have not been described.

Length 5.0-9.0 mm. Shape elongate-oval. Color brown to reddish-brown, without metallic reflections. Head prognathus, not deflexed. Antennae straight (not geniculate), 10-segmented with 3-segmented, unopposable club (all segments tomentose). Eyes with acone ommatidia, lacking canthus. Clypeus lacking tubercle or horn. Labrum concealed beneath clypeus. Mandibles prominent, quadrate or rounded at apex, produced beyond apex of labrum. Maxillae with 4-segmented palpi; labium with 4-segmented palpi. Pronotum weakly convex, base narrower than elytral base, lacking tubercles, ridges, horns, or sulci. Elytra elongate, weakly convex, with weakly impressed, punctate striae. Pygidium concealed by elytra. Scutellum exposed, parabolic. Legs with protrochantin exposed, procoxae subconical, mesocoxae virtually contiguous; protibiae serrate on outer margin, apex lacking articulated spur; meso- and metatibia with ridges, apices with 2 spurs; spurs mesad, adjacent (not separated by basal metatarsal segment); tarsi 5-5-5; claws equal in size, simple; empodium present, extending to apex of fifth tarsal segment, with 2 setae. Abdomen with 7 visible sternites; 7 functional abdominal spiracles situated in pleural membrane. Wings well developed in male (vestigial in female), M-Cu loop and one apical detached vein present. Male genitalia trilobed. References: Holloway 1972; Scholtz 1990.

Classification Status
The genus Diphyllostoma was originally placed in the family Lucanidae by Fall (1901) based on the 10-segmented antenna and lack of an eye canthus (typical characteristics of the family Lucanidae). However, several significant characters of Diphyllostoma are not found in other members of the family Lucanidae or other scarabaeoids. These include abdomen with 7 ventrites, exposed second abdominal segment, exposed protrochantin, and protibial spur lacking. Holloway (1972) proposed the family Diphllyostomatidae for the genus Diphyllostoma because of these unique characters.

Based on comparative studies, Holloway (1972) suggested the Diphyllostomatidae may be most closely related to the family Geotrupidae. Browne (1993), Scholtz (1990), and Browne and Scholtz (1995) hypothesized that the Diphyllostomatidae is the sister group to the Lucanidae. Diphyllostomatid and lucanids comprise the sister group to a clade that includes the families Glaphyridae, Trogidae, Pleocomidae, and Bolboceratidae.

The genus Diphyllostoma includes three species that are found only in California in the western United States (Fall 1901, 1932).

New World Genus of Diphyllostomatidae

Females differ from males in having greatly reduced eyes and vestigial wings. Life history information is scant. The adults are diurnal.

Immatures are not known but are probably of the scarabaeoid form and probably live in the soil.

References Cited
BROWNE, D. J. 1993. Phylogenetic significance of the hind wing basal articulation of the Scarabaeoidea (Coleoptera). Ph.D. Thesis, University of Pretoria, Pretoria, South Africa.

BROWNE, D. J. and C. H. SCHOLTZ. 1995. Phylogeny of the families of the Scarabaeiodea (Coleoptera) based on characters of the hindwing articulation, hindwing base and wing venation. Systematic Entomology 21: 145-173.

FALL, H. C. 1901. Two new species of Lucanidae from California. Canadian Entomologist 33: 289-292.

FALL, H. C. 1932. Diphyllostoma: a third species. Pan-Pacific Entomologist 8: 159-161.

HOLLOWAY, B. A. 1972. The systematic position of the genus Diphyllostoma Fall (Coleoptera: Scarabaeoidea). New Zealand Journal of Science 15: 31-38.

SCHOLTZ, C. H. 1990. Phylogenetic trends in the Scarabaeoidea (Coleoptera). Journal of Natural History 24: 1027-1066.