Schizognathous and holorhinal birds with heterocoelous vertebrae and 14 or 15 cervical vertebra. The sternum has a single notch on each side of the posterior margin; oil-gland tufted; caeca well developed ; besides the ambiens, the femora-caudal, accessory femoro-caudal and semitendinosus muscles are always present; the accessory semitendinosus is present in the Rallidae, not in Heliornithidae,
Key to Families.
A. Rectrices 10 to 14, usually 12; an aftershaft present …………Rallidae, p. 3.
B. Rectrices 18; no aftershaft…………Heliornithidae, p. 36,