Geocenamus angelescresti n. sp., a Diagnostic Key and Compendium to the Species of the Genus Geocenamus Thorne &Malek, 1968 (Nematoda: Belonolaimidae).

Geocenamus angelescresti n. sp. (Nematoda: Belonolaimidae) was found in rhizosphere of Pinus ponderosa and Arctostaphylos patula growing along Angeles Crest Highway in the San Gabriel mountains of California. The nematode species is characterized by a round-to-hexagonal labial disc with six bulging sectors, lateral sectors of first labial annule smaller than the submedian sectors, six to eight labial annules, distinct deirids, stylet length (45-57 microm), body length (666-996 microm), lateral field with or without areolation of outer bands on tail, and a rounded, smooth tail terminus. Geocenamus angelescresti n. sp. most closely resembles G. superbus but differs from it by a shorter stylet (45-57 microm vs. 67 microm), shorter body length (666-996 microm vs. 1,200 microm), bulged sectors and smaller diameter of the labial disc (2.3-2.8 microm vs. 4.0 microm, round, smooth), longer female tail (54-68 microm vs. 41 microm), and a narrower tail terminus. An emended description of the genus and a list of valid species are provided. Geocenamus arcticus (Mulvey, 1969) Tarjan 1973 and G. uralensis Baydulova 1983 are proposed as junior synonyms of G. tenuidens Thorne &Malek 1968. An identification key to 12 species of Geocenamus and a compendium of important diagnostic morphological characters used in the identification of species are included.