THE GENUS CHORDEILES SWAINSON — OBERHOLSER. 15 



Chordeiles virginianus the subspecies are properly placed in their 

 phylogenetic order as far as the fourth, for Chordeiles virginianus 

 aserriensis is surely a pale form derived from Chordeiles virginianus 

 chapmani. But Chordeiles virginianus virginianus is without doubt 

 also an offshoot from Chordeiles vi7yiiuanus chapmani, and subspecifi- 

 cally not very closely allied to Chordeiles virginianus aserriensis. The 

 rest follow in their presumed natural order. 



In Chordeiles acutipennis a practically natural order is possible, 

 the only races which require comment in this connection being 

 Chordeiles acutipennis acutipennis and Chordeiles acutipeniiis exilis. 

 Were the linear sequence to be strictly geographical, that of the first 

 three races of Chordeiles acutipennis would be Chordeiles a. exilis^ 

 Chordeiles a. acutipennis, Chordeiles a. micromeris; for the first is 

 geographically isolated from the Central American form not only by 

 a hiatus in the breeding range but by the interpolation of Chordeiles 

 acutipennis acutipennis. This race, Chordeiles acutipennis exilis,^ is, 

 however, in some characters a departure from Chordeiles acutipennis 

 acutipennis in the direction of Chordeiles acutipennis micromeris, 

 though not exactly intermediate, and is probably the result of envi- 

 ronmental conditions somewhat similar to those of the last-mentioned 

 form. 



In the case of Chordeiles rupestris, the material is so limited that 

 only a suggestive opinion is possible. If all the characters of Chor- 

 deiles rupestris xyostictus ^ and Chordeiles rupestris zaleucus^ par- 

 ticularly of the latter, prove constant in a larger series^ the former is 

 probably the one most closely allied to Chordeiles rupestris rupestris, 

 since it differs only in colors, whereas Chordeiles rupestris zaleucus 

 differs also in pattern of coloration. 



Species and subspecies. — There seem to be only three specific types 

 referable to the genus Chordeiles, namely, virginianus, acutipennis, 

 and 'rupestris; but these are so trenchantly different from each other 

 both structurally and in pattern of coloration that there can be no 

 question of their entire distinctness. All the other forms are clearly 

 subspecies. The 17 forms here recognized are distributed as follows : 

 Chordeiles virginianus, with 9 races ; Chordeiles acutipennis, with 5 ; 

 and Chordeiles rupestris, with 3. For convenience of reference a list 

 of all tliese, with their type localities, is added here : 



^ See p. 98. 



2 See p. 116. 



3 See p. 118. 



