68 -. PYRANNIDA. 
determining the various species abound in their writings. The most recent of these is 
Mr. Ridgway’s, who, in his ‘ Manual of North-American Birds,’ gives a key whereby to 
determine the North-American and Mexican species. This key was adopted almost in 
its entirety by Mr. Sclater in the fourteenth volume of the Catalogue of Birds in the 
British Museum, and we have studied it closely for our present work. If we except 
the use of subspecific names the result we come to is not very different from Mr. Ridg- 
way’s, though we arrive at our conclusions by rather different means. We have not taken 
much account of comparative measurements, for experience shows how greatly these 
vary in the members of the same species. — . | 
In endeavouring to determine Mexican and Central-American individuals of the 
migratory Hmpidonaces, we are met with the difficulty arising from having to compare 
birds of different seasons together. By far the greater part of the birds collected in 
the south are obtained in the winter and early spring months, 7. ¢. in the dry season. 
In the States, collecting commences on the arrival of the spring migrants and 
extends through the summer. Thus the only birds that are properly available for 
comparison, so far as their plumage is concerned, are those shot in the latter part of 
the spring in the south just as they are preparing to leave, and those just arrived in the 
north from the south. Our materials do not always include birds prepared under these 
conditions. 7 
Our task, however, has been vastly lightened by having before us the collection of 
Messrs. Henshaw and Merriam with its extensive series of carefully named specimens 
of North-American species. 
Empidonax is almost exclusively a genus of America north of the Isthmus of Panama. 
There are a few species located in the north-western parts of South America, and a 
small section occurs as far south as the Argentine republic; but it is doubtful if the 
latter do not belong rather to Empidochanes. 
Of eighteen species recognized by us, no less than fourteen occur within our limits, 
of which perhaps eight may be wholly or partially migrants, leaving six residents. The 
birds that perform the longest migrations are E. acadicus, E. trailli, E. minimus, 
EL. flaviventris, and E. hammondi. The partial migrants are E. fulvifrons, E. bairdi, 
and £. obscurus. Mexico retains as residents E. affinis and E. canescens, Guatemala 
E. salvini, Mexico and Central America generally 2. albigularis, Costa Rica and Panama 
L. flavescens and LE. atriceps. 
Like Tyrannus, Empidonax has short stiff setose feathers, which almost hide the 
open nostrils, and the rictal bristles are well developed but not so long as in Mitrephanes ; 
the bill is wide, the width at the rictus being rather more than half the length of the 
tomia, the sides of the bill are convex from the base to the tip; the tarsi are slender; 
the 3rd quill is the longest in the wing, the 2nd=4th, lst=6th ; tail moderate, ># 
wing, wing >4 tarsus. 
