140 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



seems to be generally conceded, however, that Professor Baird was right 

 in this determination ; therefore, as Dr. Cones snrmises (Pr. Ac. Nat. Sci. 

 Phila. 1872, p. 68), Tyrannula mexicana, Kaup, and T. cooperi, Kaup, 

 must have been based upon variations of one species — the one under con- 

 sideration ! 



In attempting to determine to which of the two forms of the species Dr. 

 Merrill's specimens belonged, I found it necessary to carefully examine all 

 the material available. This consisted of twenty-four specimens, belong- 

 ing chiefly to the collection of the National Museum. After taking care- 

 ful measurements of every specimen, and submitting all to the closest 

 scrutiny and comparison, I found myself forced to a conclusion different 

 from that reached by Dr. Coues (see Bull. U. S. Geol. and Geog. Surv. 

 Terr. IV, No. 1, pp. 32, 33), in whose opinion regarding the matter I had 

 previously coincided. I now find, that (1) while extreme exami)les of 

 var. cooperi are astonishingly different from erythrocercus proper, such 

 individuals form a very small proportion of the whole, and are chiefly 

 from Western and Southwestern Mexico, where several other species of 

 birds, notably Pyranga cestiva (var. cooperi, Ridgw.), attain the same 

 great development of the bill (and, in fact, all the measurements); that 

 (2) nearly all specimens from Mexico and Guatemala should be referred 

 to cooperi, examples referable to erythrocercus on account of dimensions 

 and shades of color being comparatively rare. Besides averaging larger 

 than var. erythrocercus, var. cooperi has usually a grayer cast of plum- 

 age, in this respect corresponding to the Mexican race of Tyrannus 

 melancholicus (var. couclii, Baird), Myiarchns knvrencii, and numerous 

 other birds of similar geographical distribution. The only satisfac- 

 tory test, however, which I have been able to apply in determining to 

 which race doubtful specimens should be referred is that of size, as 

 follows : — 



Var. ERYTHROCERCUS. — Wing, 3.40-3.95 (average, 3.77) ; tail, 3.60- 

 4.00 (average, 3.82); bill, from nostril, .55-68 (average, .61); tarsus, 

 .85-.88 (average, .86).* Eah. — Eastern Tropical America, from Para- 

 guay to Southern Mexico, but chiefly southward of the latter country. 



Var. COOPERI.— Wing, 3.85-4.45 (average, 4.15); tail, 4.00-4.60 faver- 

 age, 4.25); bill, from nostril, .00-.82 (average, .69); tarsus, .88-.95 (av- 



Six specimens, as follows : — 



16348 

 16:i49 

 d!)423 

 39210 

 39213 

 57649 



? ad. 



— ad. 



-ad. 

 d ad. 



— ad. 

 d ad. 



TJ. S. 

 U. S. 



U.S. 

 U.S. 

 U. S. 

 U.S. 



Localitv. 



Date. 



"Brazil " 



Paraguay 



Co.sta Rica 



Merida, Yucatan 



. -do 



Sta. Eflgenia, Tehuan tepee. 



Aug. — , l^fiO I 3. (i.j 

 May — , 1809 , X I'l 

 ....' I 3. 90 



May 90,1805 I 3.95 

 Apr. 9, 1865 3. 4') 

 Dec. 18, 1868 i 3. 95 



