576 ON THE DICEUEID^ AND THEIR AEEANGEMENT [1878. 



The nasal and frontal plumes occur, according to the species, in every stage of development, 

 reaching to a fully webbed, lengthened, and voluminous overhanging frontal crest in B. grandis ; 

 while in Chihia hottentotta the nasal plumes are even more lengthened, but the webs of the 

 longest are obsolete. A parallel instance in other genera occurs in Edoliiis forficatus, in which 

 species the nasal plumes are developed into a short erect bunch of webbed feathers, while in 

 Buchanga andamanensis the erect shafts are webless. The tendency^of the outer pair of rectrices 

 to twist, whereby the full growth of the inner is probably checked, is indicated in every species 

 in which the outer pair is abnormally lengthened relatively to the remaining pairs. The amount 

 and distribution of the metallic burnishing on parts of the plumage is another direction in which 

 specific variation exhibits itself. Now if, instead of an exaggeration or abortion of a frontal 

 crest for instance, the variation of a species showed itself by some constant mark of a different 

 colour, or even shade of the same colour, the specific distinctness of the species possessing it 

 would be readily admitted. Mr. Sharpe ignores such differences — for example, in the genus 

 Dissemurus, and unites all the races which have been separated by previous authors ; and yet he 

 makes a new species, D. ceylonensis, upon grounds even less sufficient. 



DiCEURUS*. — Under this genus Mr. Sharpe places three African species, and associates them 



with two Philippine and a Malaccan species which extends to the Himalayas. We thus have the 



Ibis 1878 small South-African I), ludivigi made congeneric with B. halicassius ; and although " tail nearly 



P- 72. square, outer feathers not curved upwards," constitutes in the key the diff'erentiating generic 



character, I), annectens with its considerably forked tail and twisted outer rectrices finds a place 



in the genus. 



Bicrurus annectens is an incipient species of a crestless Bissemurus, on the confines of which 

 genus it should be placed. 



Bicrurus atripennis, B. modestus, B. ludwigi. — These three African species cannot be 

 generically separated from B. assimilis (ranked as a Buchanga in Mr. Sharpe's Catalogue). The 

 four known African species of the family form a natural group with subfurcate tails, and should 

 be kept distinct under Reichenbach's title Musicus. The continental Bicrurus coracinus is not 

 kept separate from the insular B. modestus, on the ground that the only tangible distinction is one 

 of dimensions. This sound principle, as will be shown further on, is not always acted upon. 



Chibia. — ^All the Austro-Papuan and Moluccan species with nearly square tails are included 

 under this genus by Mr. Sharpe. The arrangement does not appear to be natural. Cliihia 

 hottentotta, the type of the genus, is an isolated form with a curved mandible. The gonys is 

 curved, and does not rise from the chin-angle in a straight line. The bird is to some extent a 

 flower-pecker, and clings to the twigs of large flowering trees, searching for its food in the calyx 

 and among the petals of each blossom ; and although little has been recorded of the habits of the 

 Papuan species, their bills are formed on a model such as that of any species of Bissemurus, and 

 apparently are not adapted for exploring flowers. "All the principal groups of the Indo-Malayan 

 islands " are brought by Mr. Sharpe within the area inhabited by the members of the genus 

 Chibia as defined by him, while China is omitted. With the exception of Lombock and Flores, I 

 am not acquainted with any Indo-Malayan island which is inhabited by any one of its members. 



* Vieillot established tliis genus in his 'Analyse,' 1816 — that is, at a date anterior to and in a work diii'erent from the 

 one quoted by Mr. Sharpe. 



