This shrew is recorded from the Sierra de Omoa in northwestern Honduras. Specimens came from moist subtropical wet forest near Cusuco National Park at 1,500–1,620 m.
The back is dark charcoal-brown, with silvery gray hair bases and dark tips; the underside is lighter. It has broad feet and long, broad claws.
Another shrew, Cryptotis merriami, was recorded at the same Cusuco locality. Compared with that species, C. mccarthyi averages a larger body and has broader forefeet and longer, broader claws.
The 2015 study measured forefoot bones from X-rays. Short, broad bones form the palm and proximal fingers; its stout upper-arm bone has enlarged projections. These skeletal features distinguish the forest neighbours.
A female was recorded as lactating on 11 December 1994, providing evidence of maternal milk production in December.
An extinction-risk assessment has not been added yet.
A field researcher reported expanding deforestation in Cusuco between visits in 2010 and 2015. The research organisation describes community forest patrols and educational work on the forest’s importance for water supplies.