either of two bat species found in the Central and South American tropics and classified as a family unto themselves. Amorphochilus schnablii is the smoky bat, whereas Furipterus horrens is also commonly called the thumbless bat. Small and delicately built, both species range in size from about 3.7 to 5.8 cm (1.5 to 2.3 inches), have tails about 2.4 to 3.6 cm (1 to 1.4 inches) in length, and weigh about 3 to 5 grams (0.1 to 0.16 ounce). These slate-gray or brown bats are notable for their reduced thumbs, which are covered by the wing membranes up to the base of their functionless claws. Both species are rarely seen, and very little is known about their habits.