The subspecies _mexicana_ has not been reported previously from Nicaragua, although Gardner _et al._ (1970:715) recently extended its known distribution southward from Honduras (Goodwin, 1942c:124) and El Salvador (Felten, 1956:180) to west-central Costa Rica. In Nicaragua, as apparently in Costa Rica, _mexicana_ occupies the Pacific versant, the Caribbean lowlands being inhabited by the smaller race, _Micronycteris megalotis microtis_ Miller, 1898 (type locality, Greytown, Nicaragua--reported also from "Río Coco," Nicaragua, by J. A. Allen, 1910:110). Nicaraguan examples of _M. m. mexicana_ are, on the average, considerably larger in cranial dimensions and length of forearm than are specimens of _M. m. microtis_ (see Table 1). The series of _microtis_ from "Río Coco," probably from the headwaters of that stream in the vicinity of San Juan de Río Coco and thus near the divide between Caribbean and Pacific drainages, is intermediate in size between the two subspecies and suggests intergradation between them. As noted also by Gardner _et al._ (1970:715), we find no differences in length of ear between _microtis_ and _mexicana_ (contrary to Miller's claim, in the original description, that _microtis_ had noticeably smaller ears), nor do we note any consistent differences in color between the two races on the basis of the specimens at hand.
Our specimens from Isla del Maíz Grande inexplicably agree rather closely in size (average but slightly smaller) with specimens of _M. m. mexicana_ from western Nicaragua and elsewhere within the range of the subspecies, and are tentatively, therefore, referred to _mexicana_. Four specimens earlier reported (G. M. Allen, 1929:130) from the same island also are relatively large (forearm 35 mm). Further commentary on this insular population must await a time when additional material is available from Central America.
_Specimens._--_Boaco_: Santa Rosa, 17 km N, 15 km E Boaco, 300 m, 1. _Chontales_: Hato Grande, 13 km S, 8 km W Juigalpa, 60 m, 1.
Only four specimens of this seemingly rare species have been recorded previously from Nicaragua--one (the holotype) from Kanawa Creek, near Cukra, north of Bluefields, 100 ft, Zelaya (Goodwin, 1942b:205), another from 12.5 mi. S and 13 mi. E Rivas, 125 ft, Rivas (Davis and Carter, 1962:67-68), and two from 6 km N Tuma, 500 m, Matagalpa (Valdez and LaVal, 1971:248). Our specimens were caught in mist nets placed over small, quiet streams that were fringed with tall, gallery forest. The surrounding areas were savanna-like with small stands of secondary forest. An adult male taken on 21 April had testes that measured 5 mm in length, whereas those of another (9 August) were 3 mm.