Of the New World, or Platyrrhine, Apes, the Marmosets come to be described first, as they have many characters which mark them out as the lowest of the _Anthropoidea_, and rank them nearer to the _Lemuroidea_ than any of the others. They are specially characterised by having only thirty-two teeth, their dental formula being I2/2, C1/1, P3/3, M2/2. In the actual number of their teeth they agree with their Eastern relations, but with this {130}difference, that in the latter the pre-molars are two, and the molars three, above and below on each side. Their flattened nose, with its wide partition between the nostrils, and their non-prehensile bushy tails, are also distinguishing characters. The face is nude, the ears large and sometimes fringed. Their hind-limbs are proportionately larger and longer than their fore-limbs, while the nails of their fingers and toes are not flattened as in the Old World Apes, but all form sharp curved claws, except on the much shortened great toe. The thumb is elongated and lies parallel, but quite unopposable to, nor indeed is it separable at will from, the rest of the digits. The fore-foot, consequently, "is a mere paw, and the term 'hand' is not applicable to it."... The plantar surface of the hind-foot "is very long, and the digits are very short. It follows from these facts that the term 'quadrumanous' is not applicable in any sense to the Marmosets." (_Huxley._) These animals have no callosities over the ischial (or buttock) bones, and no cheek-pouches. In their smooth and rounded skull superciliary ridges are conspicuously absent; and the ear-capsules have, as has been already observed, no external bony canal for conducting sound vibrations to the inner ear. The hyoid bone resembles that of the Lemurs. This family has been divided into two genera, distinguished from each other only by a variation in the relative length of their incisor and canine teeth, which is so slight as to render it doubtful whether these differences really warrant the generic separation of the two groups. As, however, the distinction has been maintained by nearly all writers upon these animals, the arrangement has been followed here, and the various species of the family will be described as true Marmosets (_Hapale_) and {131}Tamarins (_Midas_). They are most numerous in the equatorial forests of South America. THE MARMOSETS. GENUS HAPALE. _Hapale_, Illiger, Prodr. Syst. Mamm., p. 71 (1811).