s, as in typical
_Vespertilionidae_, the second of these is elongated and in
_Thyroptera_ divided into two, as in _Phyllostomatidae_.

[Illustration: FIG. 17.--Head of _Chilonatalus micropus_. x2. (From
Dobson.)]

The first two genera, _Furipterus_ and _Amorphochilus_, each have a
single species, the latter being distinguished from the former by the
wide separation of the nostrils and the backward prolongation of the
palate. In both the crown of the head is elevated, the thumb and first
phalange of the middle finger are very short, and the premolars are
2/3. The same elevation of the crown characterizes the genera
_Natalus_ and _Chilonatalus_ (fig. 17), in which the premolars are
3/3: in general appearance these bats are very like the Old World
vespertilionine genus _Cerivoula_, except for the short triangular
tragus. Lastly, _Thyroptera_ includes two species distinguished by an
additional phalange in the middle finger and by accessory
clinging-organs attached to the extremities. In _Thyroptera tricolor_,
_i._ 2/3, _p._ 3/3, from Brazil, these have the appearance of small,
circular, stalked, hollow disks (fig. 18), resembling miniature
sucking-cups of cuttle-fishes, and are attached to the inferior
surfaces of the thumbs and the soles of the feet. By their aid the bat
is able to maintain its hold when creeping over smooth vertical
surfaces.

[Illustration: FIG. 18.--Suctorial Disks in _Thyroptera tricolor_,
_a_, side, and _b_, concave surface, of thumb disk; _c_, foot with
disk, and calcar with projections (all much enlarged). (From Dobson.)]

The second or typical subfamily, _Vespertilioninae_, includes all the
remaining members of the family with the exception of the aberrant
_Molossinae_. The upper incisors are in proximity to the canines; the
premaxillae widely separated; the ears medium or large; the dental
formula is _i._ 2/3 (or 1/3), _c._ 1/1, _p._ 3/3 (2/3, 2/2, or 1/2),
_m._ 3/3; and the fibula very small and imperfect. All the members of
this large cosmopolitan group are closely allied, and differ chiefly
by external characters. They may be divided into subgroups. In the
first of these, the _Plecoteae_, of which the long-eared bat
(_Plecotus auritus_) is the type, the crown of the head is but
slightly raised above the face-line, the upper incisors are close to
the canines, and the nostrils are margined behind by grooves an the
up