1920] 



Swarth: Revision of Avian Genus Passerella 



83 



in this method of ascertaining the age of birds, and it is upon this basis 

 only that autumn specimens of Passerella are listed in the present 

 paper as immature or adult. In the case of material obtained from 

 outside sources the age of autumn specimens is not indicated in these 

 lists even though marked upon the label, unless the collector is known 

 to have used the same method. Midsummer birds, however, are entered 

 as "adult," as distinguishing breeding individuals from juveniles. 



Color terms are from Ridgway (1912). 



Measurements are in millimeters, and taken as follows :* 



Length of wing. — A straight line from the bend of the closed wing 

 to the tip of the longest primary, with these feathers 

 in their natural position (not straightened). 



Length of tail. — From the point of insertion of 

 the middle rectrices to the tip of the longest. 



Culmen. — Measured in a straight line from a 

 point where the feathers cease to hide the culmen, 

 to the tip of the maxilla, the line & c on the accom- 

 panying diagram (fig. A). The unfeathered ridge 

 of the culmen extends backward a little way be- 

 tween rows of overlapping feathers which cover it, 

 but the measurement back to the edge of the first 

 intercepting feather base is no more constant than 

 the slightly variable standard above indicated. 



Depth of hill. — From the base of the culmen as 

 above indicated, to the angle formed by the feathers 

 at the lower edge of the ramus of the mandible. 

 The measurement secured by placing the points of the calipers at b 

 and a, as indicated on the accompanying diagram (fig. A). 



Width of hill. — Measured at the base of the lower mandible, the 

 line d e as shown on the diagram (fig. A). 



Tarsus. — A straight line from the center of the heel joint on the 

 posterior side to the joint between the metatarsus and the middle toe 

 on the anterior side. In Passerella the lower point indicated is at 

 the lower edge of the last scale that completely covers the front of 

 the "shin." (See fig. B, atoh.) 



Hind toe with claw. — Measured along the under side, from the 

 joint between the hind toe and the metatarsus to the tip of the claw. 

 (See fig. B, e to d.) 



Fig. A. Show- 

 ing methods of 

 taking measure- 

 ments of the bill 

 used in this paper. 

 b to c, length of 

 culmen ; b to a, 

 depth of bill; d 

 to e, width of bill. 



* These measurements are based upon the system used by Oberholser (1912, 

 p. 533), but with modifications, as indicated. 



