Holotype (♂): “GUYANA: Region VIII/ 5°17.823'N, 59°50.000'W; 684 m/ Ayanganna Airstrip, trail from Blackwater Creek Camp to Potaro River/ small forested creek with lots of detritus/ 20.iii.2014; leg. A. Short/ GY14-0320-01A” (CBDG). Paratypes (1): GUYANA: Region VIII: same data as holotype (SEMC, DNA voucher SLE 1079).

Primocerussemipubescens can be recognized by the presence of sharply impressed elytral punctures, with serial punctures well differentiated (larger and deeper than remainder punctures), longitudinally aligned to form elytral striae. It can be differentiated by the hydrofuge pubescence of the metafemora covering less than basal half of the anterior surface (covering at least basal 3/4 in P.petilus and P.striatolatus).

Body length 3.7 mm, width 2.0 mm. Body elongate oval, strongly convex (Fig. 13G, H). General coloration dark brown. Elytra with ground punctures sharply marked, and well-defined rows of serial punctures (forming elytral striae); elytral striae not impressed along elytra. Posterior elevation of mesoventrite with simple transverse ridge. Metafemora with hydrofuge pubescence covering less than basal half of anterior surface (Fig. 13I). Apex of fifth abdominal ventrite truncate.

Named from the Latin word semis, meaning half, combined with the word pubescens, in reference to the hydrofuge pubescence covering only half of the anterior surface of the metafemora in this species.

Primocerussemipubescens has only been collected around the Ayanganna airstrip in Guyana, 684–687 m in elevation (Fig. 15B).

The known specimens were collected along the margins of a sandy creek that had lots of detritus.