Zoological Society, 521 



there are species. Take, for instance, the two very natural groups 

 Corvus and Parus, as now restricted ; it will be found on examina- 

 tion that there are marked differences of both structure and habits 

 which characterize almost every one of the species. It is plain then 

 that we have in general no other guide in the definition of new ge- 

 nera than a mere opinion as to the amount of structural variation 

 which is considered to authorize their adoption, and I think there 

 can be no doubt that in many of the genera recently established in 

 ornithology, the standard has been reduced too low ; in other words, 

 these genera are based on diversities of structure of so little value as 

 to be practically inconvenient. All genera profess to be of equal 

 rank, and we should therefore aim at making them as nearly so as 

 possible, and at the same time not inconveniently numerous. 



" Granting, however, that many of the existing genera of birds are 

 based on insufficient characters, and may require to be reincorporated 

 with the groups from which they have been divided, it is equally 

 certain that other groups exist in our cabinets, whose characters, as 

 yet undefined, are so marked, as to demand in fairness, and with the 

 view of producing equality of rank, to be defined and named as ge- 

 nera. A few of these groups I now bring forward, illustrated by 

 specimens from my own cabinet, and the meeting will be able to 

 judge how far the structures here exhibited appear to authorize 

 generic distinction. 



" I also take this opportunity of exhibiting a specimen of that rare 

 bird the Glyphorhynchus cuneatus (Licht.), afterwards named Xeno- 

 phasia platyrhyncha by Mr. Swainson. This bird has the tail of 

 Dendrocolaptes and the general form of Xenops, while the beak is 

 altogether anomalous, being compressed at the sides and depressed 

 at the apex." 



Fam. Sylviad^e. 



Subfam. Ma luring. 

 Genus Sphenosacus*, n. g. 

 < Motacilla, Gm., ■< Malurus, Sw., < Sphenura, Licht. 

 DifF. Char. — Beak much compressed ; tail cuneate. 



Rostrum mediocre, compressum, ad basin elevatum, culmine sub- 

 recto, juxta apicem deorsum, gonyde pariter sursum curvato, to- 

 mio maxillari emarginato, commissura leviter deflexa. Nares 

 oblonga?, membrana supra tectse. Vibrissa? nullae. 



Alee breves rotundatse, remigibus 4 a , 5a, 6a, 7a, aequalibus, primam 

 duplo excedentibus. 



Cauda longiuscula, maxime cuneata, rectricibus strictis, acutis, sub- 

 decompositis, intermediis exteriores triple- superantibus. 



Pedes fortes, tarsis longiusculis, acrotarsiis scutellatis, paratarsiis 

 integris, digitis lateralibus sequalibus. 



Ungues modice curvati, acuti. 



Ptilosis rigida, pennis subdecompositis. 

 Habitat in Africa. 

 Species unica, S. Africanus (Gm.), Levaill. Ois. d'Af., pi. 112. f. 2. 



(Sphenura tibicen, Licht.) 



* 20>}v, a wedge ; ola%, a helm. 



