The Colymbiformes constitute a very archaic Order of Birds, and hold a somewhat isolated position. Older writers combined them with the Alcidae as a group Pygopodes, but recent anatomical investigations make it clear that Auks have more affinity to Gulls, which again trend to the Limicoline alliance. As regards structure, the two Sub-Orders COLYMBI and PODICIPEDES, with their Families _Colymbidae_, or Divers, and _Podicipedidae_, or Grebes, may be here treated together. They are all water-birds with webbed or lobed toes and extraordinarily flattened metatarsi. The sternum in the Colymbidae is much longer than broad, in the Podicipedidae short and wide, while the furcula is Y-shaped; the neck is more or less elongated; the bill in the former Family is strong, straight, acute, and compressed, in the latter moderate and sometimes recurved, being either slender, as in _Aechmophorus_, or very stout, as in _Podilymbus_. The scutellated metatarsi are set very far back, and are fairly long, the procnemial process of the tibia being remarkably elongated, though Grebes alone have a distinct patella; the hallux is very small and has a small membrane, {50}but whereas Divers have the anterior toes fully webbed, their allies have them surrounded by large lobes of skin, connected only at the base. The claws are abnormally broad and flat in Grebes, the outer margin of the third being serrated. In the Colymbidae the wing is short, narrow, and pointed, with eleven primaries and about twenty secondaries; in the Podicipedidae it is still shorter and concave in form, with twelve primaries but rarely twenty secondaries; in the latter no true rectrices can be distinguished, though a tuft of downy feathers exists, while in the former they are normal though much reduced, and number from eighteen to twenty. Grebes have bare lores, and are frequently adorned in the breeding season with crests or tippets of a golden or brownish colour; the dense glossy plumage being more commonly used for decorative purposes than the duller coats of Divers. The tongue is always long and pointed, the syrinx is tracheo-bronchial, the nostrils are pervious, an aftershaft is present, and both adults and young are uniformly downy. Fossil remains from the Oligocene of France and southern England, indicating a genus intermediate between the two Families, have been named _Colymboïdes_.[50]