On the Genus Icterus ofM. Brisson. 



197 



mine in detail the remaining subfamilies of the Siurnidce, which 

 seem, as far at least as my present views extend, to be repre- 

 sented by the genera Pastor, Temm., Lamprotornis, Temm., 

 Buphaga, Briss. and Sturmis, Auct. I cannot therefore say with 

 accuracy what are the normal and aberrant groups of the present 

 subfamily. Such groups can never be decidedly recognised in any 

 assemblage of natural objects until the characters of the adjoining 

 assemblages are equally determined. The characters of all must 

 be compared together in order to decide which of the groups 

 in the assemblage under consideration are most distinguished from 

 the adjoining assemblages, or in other words which are most nor- 

 mal in their own ; and which of them on the other hand most 

 nearly approach the same neighbouring assemblages, or, scienti- 

 fically speaking, which are most aberrant. I shall draw out how- 

 ever the following table of the groups which have come before us 

 in the present sketch, in order to point out at one view the mode 

 in which their characters vary, and yet pass gradually into each 

 other. And at the same time I shall suggest, although with a mark 

 of doubt, the normal and aberrant sub-divisions ; the predominant 

 characters of the present subfamily appearing to me, as far as I 

 can judge from a primary view of the group, to consist in the 

 strength, straightness, and conical form of the bill, as exhibited in 

 Le'zstes and Cassicus ; while the character of the base of the bill 

 passing backwards over the front of the head, being carried appa- 

 rently to the extreme in Cassicus, seems to point out that genus 

 as the most normal or typical of all. 



Normal group ? 

 Rostro crasso, recto. 



CRostro recto, basi angulato. 

 j Cauda fere aequali. 



Leistes. 



Aberrant group ? 



Rostro aut crasso at cur- 

 vato, aut debili. 



j Rostro recto, basi rotundato. Cassicus. 



(^ Cauda subisquali, 



I'Rostro crasso, curvato, basi Quiscahjs. 



angulato. Cauda gradata, 

 cynrtbiformi. 



Rostro curvato, debili, basi Icterus. 



angulato. Cauda gradata, 

 rotundata. 



Rostro debili, recto, basi an- Xanthornbs, 



^gulato. Cauda subrotundata. 



[To be continued.'] vj ^ # 



