196 Mr. Vigors's Sketches in Ornithology/. 



l(nd frotn those which succeed by ths strength of that member; 

 w+iile it differs from all ia the keel-like construction of the tail. 

 By the curvature of the bill it accords with the succeeding genus 

 Icterus^ a group also which of all the subfamily most nearly ap- 

 proaches it in the lengthened and graduated form of the tail. 

 The strength of the bill is now lost in the groups on which we 

 next enter, and the weakness of that member becomes the predo- 

 minant character. This character is conspicuous in Icterus^ and 

 Is carried on to the following group oi Xanthornus^ uniting the twd 

 genera together, and distinguishing them from all the others. 

 The curvature of the bill however which united Quiscalus with Icte-^ 

 rus, is lost in Xanthornus^ where the straight bill is again resumed. 

 The lengthened and graduated tail of Icterus is also superseded by 

 the slightly rounded tail of Xanthornus, The straightness of the bill 

 now predominates, and unites this last mentioned group to Leistes : 

 while the tail also slightly rounded in Xanthornus accords with 

 the nearly even tail of Leistes. In the latter genus however the 

 bill again becomes strong : and a different construction of thfe 

 wing separates the group from the rest of the subfamily, the four 

 first quill feathers being the longest, and all nearly of equal 

 length. The strength and straightness of the bill of Le'istes in the 

 last place brings us round again to the group of Cassicus, which, 

 as has been already observed, exhibits a sufficiently distinct pecu- 

 liarity of character in the rounded form of the base of the bill. 

 The typical species of Cassicus also differ from those of Le'istes 

 in the shape of the wing. But an extreme species of Cassicus^ 

 the C. niger^ intimately according with the type of its own group 

 in every other particular, deviates from it in this latter character, 

 and assumes the wing of Le'istes^ the four first quill feathers 

 being nearly even in length, and longer than the rest. A beaiu- 

 tiful interchange and gradation of character is thus conspicuous 

 throughout the subfamily; where the typical species of each 

 group exhibit ii, decided difference in character, and yet where 

 the extreme species of all approach so closely to each other, as 

 scarcely to admit of our drawing a line of demarcation between 

 them. 

 . I have not as yet had sufficient leisure or opportunity to e*a- 



