• Webster's Revised Unabridged Dictionary
    • n. pl Monodelphia (Zoöl) The group that includes all ordinary or placental mammals; the Placentalia. See Mammalia.
    • ***
Century Dictionary and Cyclopedia
    • n monodelphia The highest of three primary divisions of mammals, or subclasses of the class Mammalia (the other two being Didelphia and Ornithodelphia); placental mammals, or Placentalia. The subclass contains all mammals except the marsupials and monotremes. The young are retained in the womb by means of placental attachment till they are well developed; the scrotum is never in front of the penis; and the uterus and vagina are never paired. The brain has a well-developed corpus callosum, and comparatively small anterior commissure. The Monodelphia are variously divided into an upper and a lower series, Educabilia or Megasthena and Ineducabilia or Microsthena; or into Archencephala (man alone), Gyrencephala, and Lissencephala; or directly into a number of orders. The orders of living monodelphians now usually adopted are eleven: Primates, Feræ, Ungulata, Hyracoidea, Proboscidea, Sirenia, and Cete, of the upper series; and Chiroptera, Insectivora, Glires (or Rodentia), and Bruta (or Edentata), of the lower series. The families are about 120 in number. Eutheria is a synonym. Also, wrongly, Monadelphia.
    • ***
Chambers's Twentieth Century Dictionary
    • Monodelphia mon-ō-del′fi-a one of the three primary divisions of mammals, the placental mammals
    • ***


Webster's Revised Unabridged Dictionary
NL., fr. Gr. mo`nos single + delfy`s the womb


In literature:

They are called the Monodelphia on this account.
"The Cambridge Natural History, Vol X., Mammalia" by Frank Evers Beddard