A new species Hydrochara simula (Coleoptera: Hydrophilidae) is described from Wis- consin and separated from other western Great Lakes species by a key. It is similar to H. obtusata (Say) and H. soror Smetana, but males can be easily recognized by a dorso-basal concavity of the aedeagus. Females can be distinguished from H. obtusata and H. soror by the more elongate penultimate segment of the maxillary palpus and other less consistent characters.
Hilsenhoff, William L. and Tracy, Bryn H.
"A New Species of Hydrochara (Coleoptera: Hydrophilidae) from the Western Great Lakes Region,"
The Great Lakes Entomologist, vol 15
Available at: https://scholar.valpo.edu/tgle/vol15/iss2/4