A male (USNM 52800) from the Escondido River above Bluefields,
originally reported by Miller and Allen (1928:203) as one of two _M.
albescens_ from that locality, provides the first record of the species
from Nicaragua and the northernmost from Middle America. The cranial
dimensions of this specimen, which compare well with those listed by
Handley (1960:467) for the Panamanian holotype and paratype, are:
greatest length of skull, 13.8 mm; zygomatic breadth, 8.9 mm;
postorbital constriction, 3.5 mm; breadth of braincase, 6.7 mm; mastoid
breadth, 7.4 mm; breadth across upper molars, 5.5 mm; length of
maxillary toothrow, 5.2 mm.
From Nicaraguan specimens of _albescens_, the skull of the specimen of
_simus_ examined (skin not seen) differs most conspicuously in having a
less inflated braincase, narrower postorbital region, and a distinct
sagittal crest.