192 BULLETIN 57, UNITED STATES NATIONAL MUSEUM. 
Genus THYROPTERA Spix. 
1823. Thyroptera Spix, Simiar. et Vespert. Brasil. Sp. Nov., p. 61 {tricolor). 
1854. Hyonycteris Lichtenstein and Peters, Monatsber. k. preuss. Akad. 
Wissensch., Berlin, p. 335 (cliscifera ) . 
1865. Thyroptera Peters, Monatsber, k. preuss. Akad. Wissensch., Berlin, 
p, 580. 
1878. Thyroptera Dobson, Catal. Chiropt. Brit. Mus., p. 345. 
Type-species. — Thyroptera tricolor Spix. 
Geographic distribution. — Tropical America, north to Honduras. 
Number of forms. — Though others have been described, only two 
species are now recognized. 
Characters. — In addition to the characters of the family the fol- 
lowing may be mentioned. Dental formula : 
-23.1.-2 3 4 5 6 7.2-2 1-1 3-3 3-3 _ 
1 2 3. 1. -2 3 4 5 6 7 4 3-3’ C 3-3’ m 3 - 3~ 38 ' 
Inner upper incisor larger than outer, but both teeth well developed, 
styliform, with small outer cusp, their 
extremities very slender and slightly 
curved inward, producing a faint sug- 
gestion of the milk dentition. Lower 
incisors 3-lobecl, the outer tooth slightly 
larger than the others. Canines weak, 
not peculiar in structure. Premolars 
both above and below, long, narrow, 
moderately high, their points very 
slender and situated at about middle 
of crown. Third upper premolar with 
remarkably developed inner ridge, ris- 
ing to a cusp anteriorly nearly as high 
as protocone of m 1 and m 2 , and show- 
ing a slight though distinct posterior 
cusp, the two together strongly sug- 
gesting a protocone and hypocone. 
First and second upper molars with 
low but evident hypocone, the other 
cusps with their commissures normal. Third upper molar with live 
cusps and three well-developed commissures. Lower molar normal, 
the outer cusps particularly high and acute. Skull (fig. 30) with 
brain case about one and one-half times as long as rostrum, abruptly 
elevated anteriorly, its surface smooth and rounded. Rostrum nar- 
row, weak, and low, the upper surface nearly flat, the sides distinctly 
inflated and translucent. Palate slightly concave laterally, nearly 
straight longitudinally. Behind tooth rows it is abruptly narrowed, 
and the posterior extension is parallel-sided. Basisphenoid region 
broadly concave, the concavity bounded anteriorly by a high trans-^ 
Fig. 30. — Thyroptera discifera. x2f 
