one hand to the subfamily _Mormopsinae_ of the _Phyllostomatidae_,
and on the other to the _Natalinae_ among the _Vespertilionidae_; both
these groups being regarded by him as of family rank.

_Mystacops_ resembles _Myzopoda_ in having three phalanges to the
middle finger, but differs in that the tail perforates the
interfemoral membrane to appear on its upper surface in the manner
characteristic of the _Emballonuridae_. The greater part of the
wing-membrane is exceedingly thin, but a narrow portion along the
fore-arm, the sides of the body, and the legs, is thick and leathery,
and beneath this thickened portion the wings are folded. Other
peculiarities of structure are found in the form of the claws of the
thumbs and toes, each of which has a small heel projecting from its
concave surface near the base, also in the sole of the foot and
inferior surface of the leg, as shown in fig. 23. The plantar surface,
including the toes, is covered with soft and very lax, deeply wrinkled
skin, and each toe is marked by a central longitudinal groove with
short grooves at right angles to it. The lax wrinkled integument is
continued along the inferior flattened surface of the ankle and leg.
These peculiarities appear to be related to climbing habits in the
species.

_Extinct Bats_.

Palaeontology tells us nothing with regard to the origin of the
Chiroptera, all the known fossil species, some of which date back to the
Oligocene, being more or less closely allied to existing types, and
therefore of comparatively little interest. The origin of the order from
primitive insectivorous mammals must have taken place at least as early
as the Lower Eocene. It is, however, noteworthy that several of the
earlier extinct species appear to be related to the _Rhinolophidae_,
which is the most generalized family of the order. Remains of
_Pteropodidae_ belonging to existing genera occur in the caves of
tropical countries in the eastern hemisphere; and the skeleton of an
extinct generic type, _Archaeopteropus_, has been obtained from the
Miocene lignite of Italy, which indicates a form to a certain extent
transitional in character between typical fruit-bats and the
insectivorous bats. The tail, for instance, which in most modern
fruit-bats is rudimentary, with only three or four vertebrae, in the
fossil has eight complete vertebrae; while the teeth of the extinct
form are distinctly cusped. Whether, however,