BIRDS OF IsrORTH AND MIDDLE AMERICA. l7l 



decidedly so; etiual to or slig-htly exceeding- in length the coinhincd 

 length of basal and middle })halange.s of middle toe. 



The absence of obvious rietal Ijristles is the only external character 

 that I am able to discover which will serve to distinguish the Icterid*, 

 as a group, from the Fringillida?. It is ti'ue that none of the IcteridtB 

 have the bill notched (i. e., the maxillary tomium notched subtermi- 

 nally), but neither do many genera of Fringillida\ With the latter 

 grouj) the Icteridte agree in the following characters: 



(1) The strongly deflexed or angulated rietal portion of the com- 

 missure (not always found in Fringillida\ howe^'er). 



(2) The abortion of the first primary. 



(8) The complete, or nearly complete, separation of the basal pha- 

 lanx of the middle toe from that of the inner toe (being united to the 

 outer toe by about half the length of the basal phalanx, as in Cor^■idffi 

 and other groups). 



(4) In having the planta tarsi closely joined along their anterior 

 edge to the acrotarsium, and with only the extreme lower portion 

 divided. 



In both groups the inner plate of the planta tarsi is depressed con- 

 spicuously below the level of the acrotarsium, the posterior margin of 

 which stands out as a prominent ridge (more conspicuously so than in 

 most Corvid^), and those of opposite sides are in close contact along, 

 th^ir posterior margin, forming a sharp posterior edge to the tarsus. 

 In ])oth groups the proportionate length of the toes themselves and the 

 relative development and curvature of the claws varies considerably 

 and to about the same extent. 



From the Sturnidte and the Ploceida% which are undoubtedly, next 

 to the Fringillidte, the most nearlv allied groups, the Icterida3 may be 

 distinguished l)y the complete abortion of the first pi'imary, both of 

 those groups being "ten-primaried." 



From the Corvida% the Icteridt\> may ])e distinguished by more 

 numerous characters, among which may be mentioned (1) the posses- 

 sion of only nine ol)vious primaries; (2) the absence of obvious rietal 

 bristles, and (3) the undivided lower portion of the planta tarsi. 



Although so nearly allied to the Fringillidte that only a single exter- 

 nal character seems available for its diagnosis, the Icteridas neverthe- 

 less constitute a well-circumscribed group, there being not a single 

 genus whose proper reference to it can be seriously questioned. At the 

 same time it is a group presenting most extreme types of teleological 

 development or adaptive modification, the strictly arboreal oropendolas 

 and caciques (genera (jrymriosthiopx^ Z((i'hynchus^ Clypicterus.^ Caclcus^ 

 etc.) representing one extreme and the terrestrial meadowlarks 

 {SfwmeJhf, Trupial'ifi^ and Leistes) the other, peculiar specializations 

 being manifested in the boat-tailed Quitiml! and spiny-tailed Doll- 

 cJiony.v. With its limited representation in North America it would 



