This very aberrant family contains only one species; the characters of the family and of the genus _Chiromys_ are, therefore, necessarily those of the single species known. THE AYE-AYE. CHIROMYS MADAGASCARIENSIS. _Sciurus madagascariensis_, Gmel., S. N., i., p. 152 (1788). _Daubentonia madagascariensis_, Geoffr., Décad. Philos., iv., p. 193 (1795); Dahlbom, Studia, p. 326, t. 12. _Chiromys madagascariensis_, Cuv., Leçons d'Anat. Comp., Tabl. de Class., 1 (1800); Owen, Tr. Z. S., vol. v., p. 33; Peters, Abhandl. K. Akad. Berlin, 1865, p. 79. (_Plate I._) PLATE I. [Illustration: THE AYE-AYE.] {15}CHARACTERS.--Head short and round; face short-snouted, with a patch of bristles below the eye, between the ear and the angle of the mouth; eyes round, prominent; eyebrows long and bristly; pupils wide, furnished with a false eyelid (a nictitating membrane); ears large, rounded, directed backwards, naked, and studded with small protuberances; tail longer than the body, bushy, with hair 3-4 inches long; hind-limbs longer than the fore-limbs, the thigh-bone being one third longer than the humerus, the hand the longest segment of the fore-limb; fingers long--the fourth the longest--with compressed and pointed claws, which are proportionately much longer than the toes; the middle or third digit slender and very remarkable, being extremely attenuated and wire-like; thumb opposable, and placed at an acute angle to the short index; great toe opposable, set at an open angle to the other digits, its nail flat; the remaining toes with pointed compressed claws (like the second toe of _Lemuridæ_ and second and third of _Tarsiidæ_). Teats, two, placed low down on the abdomen. Length of body and tail together 36 inches. Skull highly arched, convex transversely; muzzle short and deep; bony palate not extending behind the middle of the posterior molar tooth; lower jaw with condyle elongated from before backwards and on a level with the cheek-teeth, its two halves united at an acute angle by elastic tissue, allowing each half to play independently of the other. Its dental formula, I1/1, C0/0, P1/0, M3/3 = 18. Incisors very large, curved, with persistent pulp, and enamel only in front, growing up as fast as worn away; canines absent (the last two characters as in the Rodents); long vacuity between incisors and pre-molar; pre-molar much smaller than molars; molars with flat crowns and very indistinct tubercules; milk-teeth agreeing more in number and form with those seen among Lemurs than with the permanent set; the upper jaw having its full set of two incisors, one canine, and a pre-molar tooth present; the lower jaw having one incisor, no canine, and one pre-molar tooth on each side. Dorsal and lumbar vertebræ together 18, sacral 3, and caudal 22-27.