34() BULLETIN 50_, UNITED STATES NATIONAL MUSEUM. 



p. Outermost (tenth) primary much shorter than sec- 

 ondaries, the next (ninth) shorter than fifth; 

 rictal bristles excessively developed, reaching 



beyond tip of bill Myiobius (p. 486) 



pp. Outermost (tenth) primary not shorter than sec- 

 ondaries, the next (ninth) not shorter than 

 fifth; rictal bristles smaller, not reaching to tip 

 of bill. 

 q. Outermost (tenth) primary equal to first, the 

 ninth equal to fifth; tail much longer than 

 distance from bend of wing to end of distal sec- 

 ondaries; no yellow on crown nor rump nor 



rufous on tail Aphanotriccus (p. 491) 



qq. Outermost (tenth) jjrimary equal to second or 

 third, the ninth longer than fifth or sixth; 

 tail much shorter than distance from bend of 

 wing to end of distal secondaries; a yellow 

 crown-spot and rump-patch and tail at least 



partly rufous Myiotriccus (extralimital)a 



mm.. Second phalanx of middle toe partly united to outer 

 toe; smaller (wing less than 55 mm.); under parts 



ochraceous-buff Terenotriccus (p. 493) 



II. Basal phalanx of middle toe not wholly united to outer toe. 

 m. Longer primaries not attenuated at tip. 



n. Bill distinctly depressed, its width at frontal antite 

 nearly equal to more than twice its depth at 

 same point; or else (Sayornis, Myiarchus, part) 

 no white or buffy superciliary stripe nor yellow 

 or orange crown-spot. 

 o. Bill broader and more depressed, its width at 

 frontal antiti' equal to or longer than gonys and 

 much more than twice its depth at same point, 

 the lateral outlines convex subbasally, concave 

 terminally, the tii> more or less distinctly cbn- 

 stricted; rictal bristles larger and stronger. 

 p. Bill smaller or shorter, the exposed culm en 

 shorter than middle toe with claw ; tarsal envel- 

 ope not typically exaspidean {Pyrrhomyias, 

 Mitrephanes) or else (DeltarhyncJius) nostrils 

 wholly exposed, opening almost vertically. 

 q. Distinctly crested; tarsal envelope not truly exas- 

 pidean (the outer side of acrotarsium not extend- 

 ing to posterior margin of tarsus, except, some- 

 times, for one or two of the lower divisions, 

 a separate series of scutella occupying most if 

 not all of the posterior margin); nostrils partly 

 concealed, narrow, longitudinal, operculate, 

 opening laterally. & 



a Myiotriccus Ridgway, Proc. Biol. Soc. Wash., xviii, Sept. 2, 1905, 207. (Type, 

 Tyrannula phcenicura Sclater.) 



'!>The tarsal envelope in these two genera is, in fact, almost quasi-pycnaspidean or 

 quasi-holaspidean, and therefore represents a decided step toward the type of scutella- 

 tion of some supposed Cotingine genera; nevertheless, there is more difference from the 

 latter than from the tarsal envelope in those genera of true Tyrannidte in which there 

 is a similar l)ut shorter series of scutella, more or less extensive but usually confined to 

 the upper half or less of the posterior margin of the tarsus. 



