'Mammalia' definitions:

Definition of 'Mammalia'

noun

Warm-blooded vertebrates characterized by mammary glands in the female [syn: Mammalia, class Mammalia]

From: GCIDE

Mammalia \Mam*ma"li*a\, n. pl. [NL., from L. mammalis. See Mammal.] (Zool.) The highest class of Vertebrata. The young are nourished for a time by milk, or an analogous fluid, secreted by the mammary glands of the mother. [1913 Webster]
Note: Mammalia are divided into three subclasses; [1913 Webster] I. Placentalia. This subclass embraces all the higher orders, including man. In these the fetus is attached to the uterus by a placenta. [1913 Webster] II. Marsupialia. In these no placenta is formed, and the young, which are born at an early state of development, are carried for a time attached to the teats, and usually protected by a marsupial pouch. The opossum, kangaroo, wombat, and koala are examples. [1913 Webster] III. Monotremata. In this group, which includes the genera Echidna and Ornithorhynchus, the female lays large eggs resembling those of a bird or lizard, and the young, which are hatched like those of birds, are nourished by a watery secretion from the imperfectly developed mammae. [1913 Webster]