Nemadus triangulum is a species in the family Leiodidae ("round fungus beetles"), in the order Coleoptera ("beetles"). It is found in North America.
References
Further reading Arnett, R.H. Jr., M. C. Thomas, P. E. Skelley and J. H. Frank. (eds.). (2002). American Beetles, Volume II: Polyphaga: Scarabaeoidea through Curculionoidea. CRC Press LLC, Boca Raton, FL. Peck, Stewart B., and Joyce Cook (2007). "Systematics, distributions, and bionomics of the Neoeocatops gen. nov. and Nemadus of North America (Coleoptera: Leiodidae: Cholevinae: Anemadini)". The Canadian Entomologist, vol. 139, no. 1, 87–117. Richard E. White. (1983). Peterson Field Guides: Beetles. Houghton Mifflin Company. Ross H. Arnett. (2000). American Insects: A Handbook of the Insects of America North of Mexico. CRC Press.