The family may be divided into two subfamilies, of which the Emballonurinae is characterized by the incomplete premaxillae, the presence of only one phalange in the index finger, and the short tail. The dental formula is generally i. 1/3 (sometimes 2/3 or 1/2), c. 1/1, p. 2/3, m. 3/3. This subfamily may be further subdivided into subgroups or sections of which the first, Embalionurae, is characterized by the slender tail perforating the interfemoral membrane, so as to appear on its upper surface; the legs long, with a slender fibula; the incisors weak; and the premolars 2/2. The typical genus Emballonura presents the following features: i. 2/3, extremity of the muzzle more or less produced beyond the lower lip, forehead flat. The genus contains several species, inhabiting islands from Madagascar through the Malay Archipelago and Siam to the Navigator Islands. Coleura, with i. 1/3, the extremity of the muzzle broad, and the forehead concave, has two species from East Africa and the Seychelles. Rhynchonycteris is distinguished from Coleura by the produced extremity of the muzzle. The single species, R. naso, from Central and South America, is common in the vicinity of streams, where it is usually found during the day resting on the vertical faces of rocks, or on trunks of trees growing over water; it escapes notice owing to the greyish colour of the fur of the body and of small tufts on the antebrachial membrane counterfeiting the weathered surfaces of rocks and bark. As evening approaches it appears on the wing, flying close to the water. Saccopteryx has i. 1/3 and the antibrachial membrane with a pouch opening on its upper surface; it contains several species from Central and South America. This sac is developed only in the male and in the female is rudimentary. In adult males a valvular longitudinal opening occupies the upper surface of the membrane leading into a small pouch, the interior of which is lined with a glandular membrane secreting an unctuous reddish substance with a strong ammoniacal odour. Allied genera are the tropical American Peropteryx and the Brazilian Cormura. The various species of tomb-bats (Taphozous) inhabit the tropical and subtropical parts of all the eastern hemisphere except Polynesia, and are distinguished by the cartilaginous premaxillaries, the deciduous pair of upper incisors, and the presence of only two pairs of lower incisors. Most of the species have a glandular sac (fig. 15) between the angles of the lower jaw, more developed in males than in females, in some species absent in the latter. An open throat-sac is wanting in T. melanopogon, but about its position are the openings of small pores, the secretion from which probably causes the hairs to grow long, forming the black beard found in many males. The three tropical American white bats, Diclidurus, with i. 1/3, c. 1/1, p. 3/2, m. 3/3, resemble Taphozous in the form of the head and ears, but, besides other characters, differ from all other bats in possessing a pouch, opening off the centre of the interior surface of the interfemoral membrane; the extremity of the tail enters this, and perforates its base.
| Fig. 15.—Heads of Tomb-Bat (Taphozous longimanus), showing relative development of throat-sacs in male and female. From Dobson. |
The second subfamily of the Emballonuridae, Rhinopomatinae, is represented only by the genus Rhinopoma, with several species ranging from Egypt through Arabia to India, Burma and Sumatra. The premaxillae (fig. 16) are complete; the index finger has two phalanges; the tail is very long and mouselike; and the dental formula i. 1/2, c. 1/1, p. 1/2, m. 2/3. Dr G.E. Dobson has remarked that these mouse-tailed bats might be elevated to the rank of a family, for it is difficult to determine their affinities, a kind of cross relationship attaching them to the Nycteridae on the one hand and to the Emballonuridae on the other. These bats, distinguished from all other Microchiroptera by the presence of two phalanges in the index finger and the long and slender tail projecting far beyond the narrow interfemoral membrane, inhabit the subterranean tombs in Egypt and deserted buildings generally from north-east Africa to Burma and Sumatra.
| Fig. 16.—Skull of Mouse-tailed Bat (Rhinopoma microphyllum). ×2. (From Dobson.) |
The last group, according to the system adopted by Prof. Max Weber, is that of the Vespertilionidae, which includes such typical bats as the pipistrelle, the noctule, and the long-eared species. By Mr G.S. Miller[1] the first section of the Typical bats. family—Natalinae—is regarded as of family rank, while the last section, or Molossinae, is included by Dr G.E. Dobson in the Emballonuridae, from the typical forms of which its members differ widely in tail-structure. In this extended sense the family, which has a cosmopolitan distribution, may be defined as follows:—The nostrils are normal and without a nose-leaf. The ethmoturbinal bones of the nasal chamber are involuted. The palatine processes of the premaxillae do not form a suture. The ear is mostly large, with a tragus. The middle finger (except in Thyroptera) has two phalanges. The fibula is usually rudimentary. The tail is long and does not perforate the interfemoral membrane. The incisors are generally 2/3 or 1/2, but may be reduced to 1/1 in the Molossinae.
| Fig. 17.—Head of Chilonatalus micropus. ×2. (From Dobson.) |
In the first subfamily, Natalinae, which is exclusively tropical American, the other upper incisors are separated from one another and from the canines; palatine processes of the premaxillae are at least partially developed; and the dental formula is i. 2/3, c. 1/1, p. (2 or 3)/3, m. 3/3. In general appearance these bats recall the more typical Vespertilionidae, although the form of the muzzle is suggestive of the Mormopsinae among the Phyllostomatidae. Again, while the form of the skull is vespertilione, the relation of the vomer to the front end of the premaxillae is of the phyllostomine type. The molars and incisors are likewise vespertilione, whereas the premolars are as distinctly phyllostomine. Finally, while the third, or middle, finger normally has two phalanges, as in typical Vespertilionidae, the second of these is elongated and in Thyroptera divided into two, as in Phyllostomatidae.
| 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 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.
| Fig. 19.—Head of Scotophilus emarginatus. (From Dobson.) |