Pseudothelphusa (Achlidon) Smalley, 1964 b: 8.
Type species. Pseudothelphusa agrestis Rathbun, 1896 [by original designation].
Diagnosis. Third maxilliped with exopod about half-length or slightly greater than half-length of ischium. G 1 slender, latero-mesially compressed, nearly straight, apical portion enlarged on caudo-mesial view. Marginal suture on mesial surface, not distorted to other surfaces. Spermatic channel opening, field of apical spines situated distally on apex; apex elongated, slim along caudo-cephalic axis.
Distribution. All species are distributed along central to southeastern Costa Rica in hydrographic basins from both the Caribbean and Pacific drainages.
Remarks. The relationships with the other pseudothephusid genera, inferred by the G 1 morphology, were considered as unclear by Rodriguez (1982), who hypothetically placed it among the Hypolobocerini.