3. =Pandion.= Outer toe reversible; claws contracted and rounded on their under surface, and not graduated in size.[41] Wing long, third quill longest; outer four with inner webs emarginated. Tail rather short, rounded. 4. =Nauclerus.= Outer toe not reversible; claws not contracted or rounded on under side, and graduated in size. Wing long, third quill longest; outer two with inner webs sinuated. Tail excessively lengthened and forked, the lateral pair of feathers more than twice as long as the middle pair. _b._ Sides of the head with a more scantily feathered orbital space, with a projecting superciliary “shield” covered with a naked skin. * A well-developed membrane, or “web,” between the outer and middle toes at the base. † Tarsus about equal to the middle toe. § Claws short and robust; two outer quills with their inner webs cut. 5. =Ictinia.= Commissure irregularly toothed and notched; front of tarsus with transverse scutellæ. Tail emarginated; third quill longest. 6. =Elanus.= Commissure without irregularities; front of tarsus with minute roundish scales. Tail double-rounded; second quill longest. §§ Claws long and slender; five outer quills with inner webs cut. 7. =Rostrhamus.= End of bill bent downward, with a long pendent hook; inner edge of middle claw slightly pectinated, or serrated. Tail emarginated; third or fourth quill longest. †† Tarsus very much longer than the middle toe. ¶ Front of tarsus unfeathered, and, with the posterior face, covered with a continuous series of broad transverse scutellæ. α. Form very long and slender, the head small, the tail and legs long and claws excessively acute; bill weak, compressed, very high through the base, the culmen greatly ascending basally, and the cere much arched; commissure usually with a very prominent “festoon.” 8. =Circus.= Face surrounded by a “ruff” of stiffened, differently formed feathers, as in the Owls. Tarsus more than twice as long as the middle toe. Wing very long, hardly concave beneath; third to fourth quill longest; outer four with inner webs sinuated. 9. =Nisus.= Face not surrounded by a ruff. Tarsus less than twice as long as the middle toe. Wing short, very concave beneath, the outer quill much bowed; third to fifth quills longest; outer five with inner webs sinuated. β. Form short and heavy, the head larger, the tail shorter, the legs more robust. Bill stronger, less compressed, lower through the base, the upper outline less ascending basally, and the cere less arched. Commissure variable.