Theria (/ˈθɪəriə/; Greek: θηρίον, wild beast) is a subclass of mammals[1] that give birth to live young without using a shelled egg, consisting of the eutherians (including the placental mammals) and the metatherians (including the marsupials). The only omitted extant mammal group is the egg-laying monotremes.
http://en.wikipedia.org/wiki/Theria
One of the four subclasses of the class Mammalia, including all living mammals except the monotremes. The Theria were by far the most successful of the several mammalian stocks that arose from the mammallike reptiles in the Triassic. The subclass is divided into three infraclasses: Pantotheria (no living survivors), Metatheria (marsupials), and Eutheria (placentals). Therian mammals are characterized by the distinctive structural history of the molar teeth. The fossil record shows that all the extremely varied therian molar types were derived from a common tribosphenic type in which three main cusps, arranged in a triangle on the upper molar, are opposed to a reversed triangle and basinlike heel on the lower molar. See Mammalia
http://encyclopedia2.thefreedictionary.com/Theriiformes
http://en.wikipedia.org/wiki/Theria
One of the four subclasses of the class Mammalia, including all living mammals except the monotremes. The Theria were by far the most successful of the several mammalian stocks that arose from the mammallike reptiles in the Triassic. The subclass is divided into three infraclasses: Pantotheria (no living survivors), Metatheria (marsupials), and Eutheria (placentals). Therian mammals are characterized by the distinctive structural history of the molar teeth. The fossil record shows that all the extremely varied therian molar types were derived from a common tribosphenic type in which three main cusps, arranged in a triangle on the upper molar, are opposed to a reversed triangle and basinlike heel on the lower molar. See Mammalia
http://encyclopedia2.thefreedictionary.com/Theriiformes