240 Mr. W. S. Rowntrce on the Dentition 



XXX. — Oti the Dentition of the Charac'inoid Genus Plabuca : 

 a neic Generic Character. By Walter S. Rowntree, 

 B.Sc, F.L.S. 



The Characinoid genus P/rtZ>i<ca is represented in the collections 

 of the British Museum of Natural History by both the recog- 

 nized species — Piabuca argentina (seven spirit-specimens and 

 one prepared skeleton) and Piabuca spilurus (one spirit- 

 specimen) ; all from Brazil. 



Careful examination of these specimens, in the course of an 

 extended study of the Characinid^ generally*, has revealed to 

 me certain dental characters which appear to have hitherto 

 escaped observation. 



The teeth in these fishes are of singular beauty, being 

 arranged in uniform series and having spatulate crescenlic 

 crowns edged with minute gold-tipped serrations. In the 

 mandible the teeth are in single series, eight in number on 

 each side. In the upper jaw a similar series of nine teeth is 

 at once apparent. The teeth are all similar in form, 

 diminishing in size towards the angle of the mouth. 



These more obvious dental characters have been recorded 

 or figured with more or less accuracy by various observers : 

 but two points of some significance have been misrepresented 

 or overlooked. These are («) the existence of additional 

 teeth, not in series with tlie others, and (6) the existence of 

 teeth in the maxilla as well as the premaxilla. 



(a) The additional Teeth. — Careful examination with the 

 aid of a lens reveals, in the premaxilla of each side, a minute 

 tooth situated in front of the general series and higher on tlie 

 gums, so that its crown is little more than level with their 

 roots. Its position is between the first and second teeth of 

 the series. These two supernumerary teeth appear from their 

 size and position to be quite useless, and their form does not 

 show the symmetrical perfection characteristic of the func- 

 tional teeth, although they are of the same general type. If 

 found in a single specimen, they might be regarded as mere 

 replacement teeth ; but the consistency with which they 

 appear in all the specimens I have examined places them, I 

 consider, in a different category. They suggest in a striking 

 way the outer series of teeth in another Characinid, Petersius 

 Jiilgendorji, which are also small and placed alternately with 

 regard to the teeth of the main series, 'i'he chief difference 

 is that in Petersius there are four teeth in the outer series 



♦ Permitted me through the kindness of G. A. Boulenger, Esq., F.R.S. 



