This subspecies differs from B. festivum hilare in having no visible microsculpture on the elytral disk (which is therefore very shiny), and in having three or more discal setae on each elytron. A very few specimens have been observed with only two setae on one elytron, but if so, the other elytron has three or more setae. For comparisons with other members of the subgenus Liocosmius, see the description of B. festivum. Specimens of B. festivum festivum tend to be larger than B. festivum hilare, and in the southern end of the range, paler.
Body length 3.5 to 4.5 mm, with most specimens longer than 3.9 mm.
Found in southern California, from just south of the Bay Area to the area around San Diego.
Found on steep sand or silt banks of creeks and rivers, often where shaded.