28 



PROF. D ARCY W. THOMPSOTi ON THE 



[Jan. 17, 



curved prefrontal processes approach very close to the postfrontnl ; 

 it is complete in the others, and its posterior portion is somewhat 

 broad and flattened, especiall}' so in A. maccio, where the broadened 

 hinder region forms an obtuse postero-inferior angle. 



Fie:. 19. 



Ara cUoroptcra. (reduced). 



The squamosal process is least developed in A. aramuna^ most 

 so in A. maraeana. The paroccipital wings are largest in A. chloro- 

 ptera and macao. The auditory meatus is widest in A. chloroptera 

 and maraeana ; it is considerably narrowed, and shows a slightly 

 projecting lower lip and a well-marked postero-superior notch in 

 A. ararauna ; and in A. macao it is very remarkably narrowed, 

 partly by the growth forwards of the posterior wall, and still 

 more by the growth backwards of the anterior, which overlaps the 

 lower part of the orifice as a broad tongue of bone. The two heads 

 of the quadrate (fig. 20) are in all more widely sepai-ate than in 



rig. 20. 



Quadrate bone of Ara chloroptera. 



A. Tiyacinthinus. The anterior margin of the infraorbital septum 

 is squarely truncate in A. ararauna ; it tends in the others, and 

 especially in A. macao, to curve forward in the same manner as, 

 though in a less degree than, in A. liyacinthinus. 



The mandible is narrowest from side to side in A. ararauna, and 

 in this respect least like that of A. liyacinthinus. In the same 

 species the articidar groove for the quadrate is nearly straight 



