THE GENUS CHOKDEILES SWAINSON OBERHOLSEE. 71 



CHORDEILES VIRGINIANUS ASERRIENSIS Cherrie. 



Chordeiles virginianus aserriensis Cherkie, Auk, vol. 13, April, 1896, p. 136 

 (Valley of Aserri River, San Jos6, Costa Rica). 



Chars, subsp. — Eesembling Chordeiles virginianus sennetti^ but de- 

 cidedly smaller ; general tone of upper parts lighter and more oclira- 

 ceous, the light areas more buffy or ochraceous (less grayish or 

 whitish) and somewhat more extensive; and the dark brown areas 

 of anterior lower surface less grayish. 



Measurements. — Male: Total length (in flesh), 223-240 (average 

 232) mm.;^ extent of wing, 573-585 (578.7).^ 



Male lowing, 179-188 (average, 183.7) mm.; tail, 94.5-105 (101.1) ; 

 exposed culmen, 6.0-7.9 (6.7) ; tarsus, 13.8-15.1 (14.5) ; middle toe, 

 13-14.8 (13.9). 



Female:- Wing, 179-185.5 (182.7) mm.; tail, 98.3-106 (102.6); 

 exposed culmen, 6.3-7.5 (6.9) ; tarsus, 13.5-14.8 (14.2) ; middle toe, 

 14-15.5 (14.4). 



Type-locality. — Valley of the Aserri River, near San Jose, Costa 

 Rica. 



Geographical distrihuiion. — Central southern Texas, and northern 

 Tamaulipas, Mexico ; south in migration to Costa Rica and probably 

 South America. Breeds in the Lower Austral Zone, north to San 

 Antonio and Rock Springs, south central Texas; west to Samuels, 

 Texas; south to Matamoros, northeastern Tamaulipas, Mexico; and 

 east to Brownsville, Corpus Christi, Wharton County, and Rich- 

 mond, central southern Texas. Migrates south through eastern 

 Mexico and Costa Rica. Winters probably in South America. 



Remarks. — This heretofore unrecognized race seems to be in color 

 most nearly like Chordeiles virginianus senndtti, though in this re- 

 spect also near Chordeiles virginianus howelli and probably in reality 

 most closely resembling this form, which it adjoins geographically. 

 From the latter it may be distinguished in the male by smaller size, 

 rather lighter, somewhat less brownish (more grayish) upper parts, 

 with less ochraceous (more whitish or grayish) markings, and 

 slightly less buffy posterior lower parts. It differs more strongly 

 from Chordeiles vii^ginianus henryi in its smaller size ; much lighter, 

 more grayish (less brownish) upper surface, with finer, much more 

 grayish and whitish (less ochraceous and tawny) light markings; 

 nearly or quite white, instead of buffy, posterior lower surface; and 

 less rufescent dark areas of the anterior under parts. 



The female of this subspecies is much more deeply buffy on the 

 posterior lower surface than is the male, and also averages slightly 



^ Three specimens. 



*Ten specimens, from Texas. 



