A microscopical examination of the teeth of Primates discloses the fact that all members of the suborder Lemuroidea possess, in a varying extent, the character of a penetration of tubes into the enamel.

In the Lemurinæ this penetration is slight, but in the Indrisinæ it is very rich.

The Galagos and Pottos also have a rich penetration, but in Nycticebus it is but feeble.

Tarsius has an enamel richly tubular, and in its structure essentially Lemurine.

A further interesting feature is that the pattern of the enamel in the Mascarene Lemurs differs from that of the Asian and African forms, and that the former has a structure identical with that found in the enamel of all Catarrhines, whilst the structure of the enamel in the Platyrrhines is identical with that found in the Asian and African Lemurs.

Two primitive Lemuroid Primates, Pelycodus and Notharctus, from the Eocene show no penetration, but in the structure of their enamel resemble the Mascarene Lemurs.

Hemiacodon, a Tarsioid Primate, also from the Eocene, has an enamel which is tubular, and in structure appears identical with the enamel of the recent Tarsius.

The enamel pattern affords a useful test of affinity if taken in conjunction with the character of a tube-penetration, and enables one to discriminate between Multituberculates, Marsupials, and Placentals.