monopnoa

from The Century Dictionary.

• noun In Owen's classification, a “subclass of Reptilia,” containing all reptiles which breathe in one way only —that is, by lungs: distinguished from Dipnoa or Branchiotoca, which breathe in two ways —that is, either by gills first and lungs afterward in the case of the same individual, or some of them by gills and others by lungs.