This group of birds is distinguishable at once from the preceding by having the ectethmoid present.
It contains, in India, six families which at first sight appear to belong to very different classes of birds. The Dromadidae, a family containing the one genus and one species, Dromas ardeola, is superficially very unlike the Gulls and Terns and certainly broke off from the Laro-Limicoline group at an early stage of its existence. Anatomically, however, it is closely related to the Gulls and even more closely to the Skuas, Stercorariidae, and also to another aberrant group, the Glareolidae. In appearance the Crab-Plover bears in many ways a superficial resemblance to Burhinus, whilst the Glareolidae contain two subfamilies, one, the Cusoriinae, birds with long legs and Plover-like carriage and secondly, the Glareolinae, birds with short legs but Plover-like flight. Ail we can say at present is that such anatomical evidence as is available shows that the families contained in the present group are nearer to one another than to any other. It may well prove, however, when more evidence is forthcoming, that both the Glareolidae and Dromadidae deserve separation from the Laro Limicolae, and should be placed in suborders by themselves, branching off at a still earlier period from the Charadriine stem.
Key to Families.
A. Three anterior toes only partially webbed.
a.Toes united at the base only with membrane. Nostrils pervious…….Glareolidae, p. 84.
b. Toes with deep web between third and fourth, smalt web only between second and third. Nostrils impervious…………..Dromadidae, p. 94.
B. Three anterior toes fully webbed.
c. Bill with cere; caeca well developed…………..Stercorariidae, p. 96.
d. Bill with no cere; caeca small and functionless.
a1. Bill not compressed.
a2 . Upper mandible larger than lower…………..Laridae, p. 100.
b2. Upper and lower mandibles about equal…………..Sternidae, p. 110.
b1. Bill very strongly compressed…………..Rhyncopidae, p. 150.