Zoological Society. 55 



only 3° 35'. And I may here observe, that in measuring both posi- 

 tions and distances, I always derange the former measurement so 

 completely, that the situation of the wire could not by possibility be 

 taken for a measure. Thus, each individual measure is not a previous 

 one, altered and amended, but is entirely new and independent. 



"It will be seen that the above observations corroborate the pre- 

 sumed motion of the star C in direction, and indicate a considerable 

 acceleration in it since 1825, compared with the mean velocity during 

 the previous forty-two years; while the distance continues very nearly 

 the same as it was at that date. Compared with Sir J. South's ob- 

 servations, the change of angle amounts to 7° 38' in six years, or 

 1°,267 per annum ; while, previously, the mean motion was supposed 

 to be only 0°,5813. But in the observations appended to the mea- 

 sures by Messrs. Herschel and South, in 1822, we were forewarned 

 to expect an acceleration, if the motion were orbitual. My observa- 

 tions of the star C, however, being made on one night only, may be 

 liable to an error of one or two degrees, especially as the position of 

 the star B, and its extreme proximity to A, render the measures of C 

 difficult." 



III. An Index to the Society's Catalogue, by Lieut. W, S. Strat- 

 ford, R.N. ; so arranged that the number of any star contained in the 

 Catalogue may be found immediately, provided there be given the 

 name of the constellation, and the letter by which the star is distin- 

 guished, or the number of the star in one of the following catalogues; 

 viz. Flamsteed's, Piazzi's, Bradley's, Lacaille's,FalIows's, Zach's, &c., 

 preference being given to each catalogue in the order of succession. 



IV. A paper containing micrometrical measurements of 364 double 

 stars, by J. F. W. Herschel, Esq. 



ZOOLOGICAL SOCIETY. 



April 26, 1831. Joshua Brookes, Esq. in the Chair. 



Mr. Vigors exhibited, from the collection of Mr. Leadbeater, an 

 undescribed species of Cockatoo from New Holland, and pointed 

 out its distinctive characters, which may be expressed as follows : 

 Plyctolophus Leadbeateri. Plyct. albus ; genis, collo in 

 Jronte, ■pectore, tectricibus alarum injerioribus, abdomineque 

 medio roseo-liftctis ; cristce elongatcc occipitalis plumis basi roseis, 

 apice albis, macula Jlava in medio uotatis ; pogoniis remigum 

 rectricumqiie internis roseis, illorum saturatioribus. 

 Statura Plyct. sulphurei, Vieill. 



Eleven species of Chcetodons, forming part of the collection of 

 Fishes from the Mauritius presented by Mr. Telfair, were laid on 

 the table. Seven of these were referable to the genus Chatodon as 

 restricted by M. Cuvier; and among them Mr. Bennett pointed out 

 more particularly the Chat, slrigangulus, Sol.; the Chict. vittattis, 

 Schn.; the Chist. Lunula, Cuv. & Val.; and two species which he 

 believed to be new to science, and which may be thus characterized : 

 Chj«t. flavescens. Chtut . flavus ; ore, fascia oculari, linea 

 pinnas dorsalem analemque jiostice ambicnte, apicequc pinnantm 



ventralium 



