THE FAMILIES AND GENERA OF BATS. 
191 
Geographic distribution . — Tropical America, north to Honduras. 
Characters .- — Shoulder joint and wing as in the Natalidae, except 
that trochiter is distinctly larger than trochin, second finger is re- 
duced to a rudimentary metacarpal less than half as long as that of 
third finger, there are three bony phalanges in third digit, and first 
phalanx of thumb bears a large sucking disk ; shoulder girdle differ- 
ing from that of the Natalidae and resembling that of the Furi- 
pteridae in the small size of the presternum, its width scarcely half 
length of presternum and mesosternum, its narrow keel slanting con- 
spicuously forward, mesosternum broad and flat, its keel obsolete, 
xiphisternum long and slender, its keel reduced to a mere ridge ; first 
and second dorsal vertebrae fused; foot abnormal, the toes with only 
two phalanges each, the third and fourth digits, together with their 
claws, anchylosed together from base to tip ; fibula reduced to a 
minute osseous thread closely applied to the tibia and disappearing 
about midway between heel ancl knee : sole with well-developed suck- 
ing disk attached to metatarsals; pelvis not essentially abnormal, 
but with very small pectineal process, and with obturator foramen 
much reduced by bony outgrowth from its sides, as in the Hippo- 
sideridae and Rhinolophidae, ischia wide apart posteriorly, a sym- 
physis pubis in males, sacrum with the posterior two vertebrae dis- 
tinct, the others fused; lumbar vertebrae distinct; skull without 
postorbital processes, much as in the Natalidae, the braincase large, 
smooth, and rounded, the rostrum slender and weak; premaxillaries 
complete, the very slender and easily broken palatal branches isolat- 
ing two foramina ; teeth normal, not essentially different from those 
of the Natalidae; ear, tragus, and muzzle as in Natalus. 
History . — As shown by the synonymy, this family has generally 
been united with the Vespertilionidae or Molossidae. Winge placed 
it with Natalus , Furipterus , and Amorphochilus to form the group 
Natalina, a section of the Vespertilionidae; and this assemblage. I 
regarded in 1899 as constituting the family Natalidae. 
Remarks . — The form of the sternum, the separate lumbar verte- 
brae, the greatly reduced second finger, the large third finger with 
fully ossified terminal phalanx, the peculiar structure of the toes, and 
the presence of sucking disk on thumb and sole are sufficient to dis- 
tinguish this family from the Natalidae. Contrary to what might be 
expected, the thumb has a well-developed claw. The Thyropteridae 
are in some respects more highly specialized than the Natalidae; in 
others, notably in the structure of the sternum and in the unfused 
lumbar vertebrae, much more primitive. As compared with the 
Furipteridae this family represents about the same stage in the devel- 
opment of the sternum; the lumbar region is more primitive; the 
feet are more highly modified, and the thumb is perhaps equally 
aberrant, though in another way. 
Principal subdivisions . — The family is represented by the single 
genus Thyroptera. 
