Produced by Gerard Arthus, Linda Cantoni, and the Online Distributed Proofreading Team at https://www.pgdp.net [Author's Edition, extracted from Bulletin of the American Museum of Natural History, Vol. IX, September 28, 1897.] ARTICLE XIX.--DESCRIPTION OF A NEW VESPERTILIONINE BAT FROM YUCATAN. By J.A. ALLEN. In a small collection of mammals recently sent by Dr. G.F. Gaumer from Izamal, Yucatan, to this Museum for identification, is a single specimen of a species of _Adelonycteris_, which appears to be undescribed. It may be called ADELONYCTERIS GAUMERI, sp. nov. Above dark brown, with an olivaceous wash, the fur being uniform dark brown to the base tipped with a slight tinge of olivaceous, the extreme tip slightly grayish in certain lights; below much lighter, the fur being dark brown basally and broadly tipped with pale buffy gray; ears and membranes black, naked, and with no trace of a whitish border. Ears of medium size, rather thin, evenly convex on the front border, slightly hollowed on the posterior border below the rounded posteriorly directed tip; tragus long and rather narrow, pointed, equal to half the height of the ear. Face semi-nude, about as in _A. fusca_. _Measurements._--"Length, 95 mm.; expanse, 286; wing, 124; tail, 40";[1] ear, 21; tragus, 11; fore arm, 39; thumb, 7; 3d digit, 79 = phal. i, 37, phal. ii, 24; phal. iii, 11; phal. iv, 7; tibia, 70; foot, 8. [Footnote 1: Collector's measurements from the fresh specimen; the rest are from the dry skin.] _Skull._--Similar in a general way to that of _A. fusca_, but about one-half smaller. Middle inner upper incisors considerably worn, and the ridges for muscular attachment strongly developed, indicating an old individual. Greatest length (front base of incisors to end of crest), 18; mastoid breadth, 8.3; zygomatic breadth, 10.1; interorbital breadth, 4; length of molar-premolar series, 4.2; palatal length, 5.3. _Type_, No. 12753/11040, [female symbol] ad., Izamal, Yucatan; collected by Dr. George F. Gaumer, for whom the species is named. In coloration _Adelonycteris gaumeri_ resembles examples of _A. fusca_ in immature dark pelage, but it differs from this species in the thinness of the ears, and in the greater relative length of the narrower and more tapering tragus, and in its very much smaller size. In size it resembles both _'Vesperugo' propinquus_ Peters and _V. (Marsipolaemus) albigularis_ Peters, respectively from Guatemala and Mexico. The peculiar structure of the ears, to say nothing of the coloration, in _V. albigularis_, render comparison with this species unnecessary. _V. propinquus_ is described as reddish above, paler and more reddish yellow below, and in this respect is widely different from _A. gaumeri_. It has also a longer thumb and foot than _A. gaumeri_.