XX INTRODUCTION. 



ear-concli is divided by a prominent keel, and the an ti tragus is re- 

 markably large in those species in which the tragus is minute 

 (Plate XXI. figs. 2, 3). In the frugivorous Megachiroptera, as 

 might be expected, the form of the ear-conch is very simple and 

 but slightly variable in all the species, and there is no tragus. 

 Although the frugivorous and sanguivorous species of Phyllostomidce 

 have a tragus, yet in them both it and the conch are remarkably 

 small and very similar in form, even in species otherwise differing 

 greatly in structure, contrasting strongly with the great develop- 

 ment of the same parts in the insectivorous species (compare Plates 

 XXIV. and XXX.). Widely, however, as the form of the ear-conch 

 differs in these groups, the common origin of aU is shown by the 

 general similarity of the structure of the tragus and by the presence 

 of a peculiar ridge of integument passing obliquely upwards and 

 forwards from the base of its inner margin on the side of the head, 

 which is equally developed in the long-headed Olossophagce and in 

 the short-skulled Stenodermata. 



In all Bats the ears are extremely mobile, each moving indepen- 

 dently at the will of the animal. This I have observed even in the 

 frugivorous Pteropodidce, in which the peciiliar vibratory movements 

 noticed by Mr. Osburn in Artibeus perspicillatus (see p. 520 infra) 

 may also be seen when the animals are alarmed. 



Dental System. 



The different forms of dentition observable in the Chiroptera will 

 be found very fully treated of in the definitions of the families and 

 genera and in the descriptions of the species, as in nearly all cases 

 the dental characters afford the most reliable guides in determining 

 their natural affinities and in their discrimination. 



Of the 400 species described in the following pages, at least 300 

 are insectivorous, and, as might be expected from the nature of 

 their food, their molar teeth are of the insectivorous type, being 

 acutely tubercular, with usually well-developed W-shaped cusps. 

 The dental formula never exceeds inc. |, c. i^, pm. t?. m — = 



b' 1 — V ^ 3 — 3' 3 — 3 



38 teeth*, but is frequently less than that number, falling as low 



2 1—1 2—2 



as inc. -J, c. j3j-, pm. :^—r^, m. 0=20 teeth in the sanguivorous group 

 Desmodontes, the variability in the number of teeth in the insecti- 

 vorous species being confined chiefly to the incisors and premolars, 



* See footuote, p. 509, for an instance of an apparent exception to this rule. 



