The Little Red-backs inhabit open unsheltered plains, and have so great a predilection for bare ground on which they can run freely about, that on their arrival on the pampas, where the earth is thickly carpeted with grass, they are seen attaching themselves to roads, sheep-pens, borders of streams, vizcacha villages, and similar places. They are exceedingly restless, running swiftly over the ground, occasionally darting into the air in pursuit of small flies, and all the flock so scattered that there will be a dozen yards between every two birds. Mr. Barrows describes their lively habits very well:--"I think this is one of the most restless birds I ever saw. You cannot depend upon him to be in the same place two consecutive half-seconds. He runs like a Sanderling, and whenever he keeps his feet still by accident, his wings are flirted in a way that shows his anxiety to be off. Several are usually found together, and sometimes a loose flock of a hundred or more is seen. They are very strong on the wing, sometimes mounting rapidly for several hundred feet, if suddenly startled, and after a few moments spent in circling like a Snipe, they drop again almost as suddenly as a shot, and as if from the very clouds." 137. PLATYRHYNCHUS MYSTACEUS (Vieill.). (BROAD-BILLED TYRANT.) +Platyrhynchus mystaceus+, _Scl. et Salv. Nomencl._ p. 44; _White, P. Z. S._ 1882, p. 605 (Misiones). _Description._--Above olive, darker on the head; coronal patch bright yellow; lores, eye-region, and ear-coverts pale yellowish; mystacal stripe blackish; wings and tail blackish edged with olive-brown; below clear fulvous, much whiter on the throat; upper mandible blackish, lower whitish; feet pale yellowish: whole length 3·3 inches, wing 2·1, tail 1·1. _Female_ similar, but no coronal patch. _Hab._ Guiana, Brazil, Paraguay, and Northern La Plata. A single example of this species was obtained by White in the forest near San Javier, Misiones. 138. EUSCARTHMUS MARGARITACEIVENTRIS (d'Orb. et Lafr.). (PEARLY-BELLIED TYRANT.) +Todirostrum margaritaceiventer+, _d'Orb. Voy., Ois._ p. 316 (Corrientes). +Euscarthmus margaritaceiventris+, _Scl. et Salv. Nomencl._ p. 45; _Salvin, Ibis_, 1880, p. 357 (Tucuman). +Triccus margaritiventris+, _Burm. La-Plata Reise_, ii. p. 456 (Paraná). _Description._--Above olive-green, wings and tail blackish edged with olive-green; whole head above, including sides and back of neck, dark cinereous; beneath pearly white, passing into pale cinereous on the sides; under wing-coverts pale yellowish, flanks tinged with olivaceous; bill hazel; feet red: whole length 4·5 inches, wing 2·1, tail 1·9. _Hab._ Paraguay, Northern La Plata, Bolivia, S. Peru, and S.E. Brazil. This species, discovered by d'Orbigny in Corrientes, was also met with near Paraná by Prof. Burmeister, and by Durnford in Tucuman. 139. EUSCARTHMUS GULARIS (Temm.). (RED-THROATED TYRANT.)