Trichodinella hesperoleuca sp.n. was found on the gills of 36 of 90 (40%) Western roach Hesperoleucus symmetricus, collected from intermittent foot-hill streams near Fresno, California. Key characteristics of the new species include: denticular ring 16 µm in diameter composed of 25 denticles, denticles 5.5 µm in length with a unique shape. Radial pins 5 or 6 per denticle. Disc to bell shaped body 34 gm in diameter. Trichodinella hespereluca differs from Trichodina due to the nature and shape of the denticles and overall size. It can be differentiated from T epizootica, the common species of Trichodinella by its size and denticular ring. Type specimens have been deposited in the USNM Helminthological collection Numbers 74370 and 74371.