Remarks on the type species of Rhigonema Cobb, 1898 (Rhigonematoidea: Rhigonematidae) and Heth Cobb, 1898 (Ransomnematoidea: Hethidae)

Additional information on Rhigonema brevicollum, the type of the genus Rhigonema, and on Heth juli, the type of the genus Heth, is presented based on original, hitherto unpublished, descriptions held in the Cobb Archive at the USDA, Beltsville, MD, USA. Both species were originally published as small annotated illustrations in a general work, although the promised full descriptions were never published by Cobb. The genus Rhigonema is shown to be based on a species lacking a vaginal diverticulum in the female genital system, but having a long, Type 2, ovejector. The genus Dudekemia, originally differentiated from Rhigonema on an assumed (and erroneous) difference in female genital tract form, is confirmed as a junior synonym of Rhigonema. A full description of both sexes of Heth juli is also provided, again based on Cobb’s original notes, thereby defining the type species with greater precision than was previously possible.