mesallantoid,a.rare.|mɛsəˈlæntɔɪd| [f.Gr. µέσ-ος middle + allantoid.] Having an allantois of intermediate size. (Cf. megallantoid, micrallantoid.) 1877W. Turner Hum. Anat. ii. 869 M. H. Milne-Edwards..has placed the Carnivora and Pinnipedia..in a Mesallantoid legion of mammals.