_Measurements._--Average and extreme measurements of seven males from the type locality, followed by those of 19 females from 38 km. SE Jesús Carranza, and finally length of forearm and cranial measurements of eight female topotypes of _M. n. extremus_, are as follows: Total length, 80 (77-82), 76 (72-80); length of tail, 32.8 (30-35), 33.5 (31-35); hind foot, 7.9 (7-8), 8.0 (8-8); forearm, 34.2 (33.6-35.3), 35.1 (33.1-36.4), 33.1 (31.8-34.3); greatest length of skull (including incisors), 13.8 (13.3-14.1), 13.6 (13.2-14.1), 12.9 (12.6-13.1); zygomatic breadth, 8.1 (7.9-8.4), 8.1 (7.9-8.3), 8.0 (only one can be measured); width of rostrum above canines, 3.2 (3.1-3.3), 3.2 (3.0-3.4), 3.1 (3.0-3.2); interorbital constriction, 3.6 (3.5-3.7), 3.6 (3.5-3.8), 3.4 (3.3-3.4); occipital depth (excluding auditory bullae and sagittal crest), 4.6 (4.4-4.8), 4.6 (4.3-4.9), 4.3 (4.1-4.6); maxillary tooth-row (C-M3), 5.0 (4.8-5.1), 5.0 (4.8-5.2), 4.7 (4.6-4.8); maxillary breadth at M3, 5.2 (5.1-5.4), 5.3 (5.1-5.5), 5.1 (4.8-5.2).
[Illustration: FIG. 1. Left side of skull, incisors, canine, and premolars × 11, and occlusal surface of left first upper molar × 20. A. _Myotis nigricans dalquesti_, holotype. B. _Myotis nigricans extremus_ No. 77674 USNM, topotype.]
_Remarks._--The subspecific name _dalquesti_ is given in recognition of Prof. Walter W. Dalquest who gathered the largest and most varied collection of mammals ever taken in the state of Veracruz.
Inspection of the measurements given above will reveal that there is no overlap between _extremus_ and _dalquesti_ in the interorbital constriction or occipital depth and only slight overlap in the length of the maxillary tooth-row and maxillary breadth.
In 10 adult females from Ocosingo, Chiapas, there is suggestion of intergradation between _dalquesti_ and _extremus_ in that one specimen (66515 KU) has the cranial characters of _extremus_ except that it is large like _dalquesti_; in two other skulls P3 is slightly displaced lingually and two other skulls bear a slight sagittal crest. These are features characterizing _extremus_. Otherwise the specimens resemble _dalquesti_, to which subspecies they are here referred.
Three males from a place 8 km. W and 10 km. N El Encino, 400 ft., Tamaulipas, are the northernmost representatives of the species and differ from the other specimens of _dalquesti_ in shorter forearm, shorter maxillary tooth-row and lesser maxillary breadth.