62 ME. W. S. EOWNTEEE ON THE 



In Serrasalmo, although, curiously and quite exceptionally, the dorsal and ventral 

 septa ajipear to be absent, there are some six lateral septa on each side which are of 

 considerable depth, and extend backwards quite to the middle of the chamber, dividing 

 the side-walls into a corresjjouding number of deep channels, continued at the anterior 

 margin into well-defined pockets or pouches which are conspicuous externally. Inter- 

 calated between these main septa are some nine much smaller septa on each side, causing 

 a further subdivision of the lateral space. I have not found any j)revious record of this 

 peculiar condition shown in fig. 4*, though the external features of the bladder have been 

 described by Valenciennes *. 



In Macrodon (PI. 3. fig. 7) the dorsal and ventral septa are large, and there are two strong 

 but shorter lateral septa with at least 30 smaller bands of very varying size intercalated. 

 The existence of lateral septa is denied by Valenciennes *, who only recognizes the two 

 median bands. In addition to the definite bands, the whole internal surface of the 

 anterior part of the chamber presents the appearance of closely-set but interrupted 

 longitudinal striae, apparently of the same character as the bands themselves. 



In Prochilorhis the dorsal septum is deep, standing out boldly ; the ventral less so. 

 Both extend to the extremity of the bladder. There are also some five lateral septa on 

 each side, which are short and of moderate dej)th. The whole bladder is very large. 



In Sarcodaces there are the two long median septa, one shorter lateral band on each 

 side, all well developed, and some three subsidiary septa on each side. 



In Ichthyohoms, Neoborus, Paraphago, and Eugiiathiclithys, very closely allied forms, 

 the two lateral bands extend to the extremity of the bladder, like the median bands, 

 than which, however, they are less prominent. There are traces of about two other 

 very faint and short lateral bands. In their near relative — Phago — the two lateral 

 bands present an appearance wliicb suggests a degeneration from the condition just 

 described ; they are unusually long, and each is continued to the extremity of the 

 bladder as a coloured streak, which is not the actual band itself, but which implies its 

 former extension. In Alestes nurse and A. macrolepidotus the median bands are strong, 

 especially the dorsal, and there are three or four short lateral sej^ta on each side. 



In Bryconaethiops and Salmimis two entire median, and two shorter lateral, septa are 

 present, all well developed and of fair depth. In Hydrocyon, Tetragonopterus, Micralestes, 

 Anostomus, Xenocliarax, Distichodus, and C/'fharimis the septa are as in the two forms 

 just previously mentioned, bvit are less distinctly raised. 



In Leptorinus and Curimatus the dorsal band is strong, the ventral apparently absent ; 

 two short weak laterals are present in Leporinm ; none in Curimatus. 



In Anacyrtus (PI. 3. fig. 8) the condition differs from that of any of the^foregoing. The 

 dorsal and ventral septa are almost obliterated, extending for only a short distance. 

 Vestiges of about five lateral bands on each side are seen running parallel to one another 

 for about half the length of the chamber, and scarcely perceptibly raised. The whole 

 lateral waU also shows a delicate network of fine, closely-set lines at right angles to one 

 another, which, however, are not jjerceptible to the touch, and do not appear to be 



* Cuvier & Valenciennes, ' Hist. Nat. des Poissons,' vol. xxii. p. 280. 



