522 PEOF. T. W. BRIDGE ON THE 



based on the misconception that previous writers had described 

 an open communication between the air-bladder and the 

 auditory organ, such as Valenciennes apparently believed to exist 

 only in Notopterus. It is now scarcely necessary to add that no 

 such open communication exists, or has even been affirmed to 

 exist, in any Pish except Notopterus Pallasii ; and, for the 

 reasons given above, it is extremely improbable that the latter 

 species offers any exception to the general rule, or, so far 

 as this point is concerned, differs in any way from its congener, 

 Notopterus iorneensis. 



VIII. COMPAEISOlSr WITH OTHER TeLEOSTS. 



Perhaps the most interesting point in the air-bladder of 

 Notopterus is the combination which it exhibits of structural 

 features, some of whicb are unique, while others are individually 

 characteristic of widely different genera or species of Teleosts. 



The extension of the air-bladder from its normal position in 

 the abdominal region into the tail is by no means of infrequent 

 occurrence in Teleosts, although it may take place in various 

 ways. In some species (e. g., species of Exocoetus) the organ is 

 prolonged backwards without undergoing subdivision into the 

 expanded hsemal canal of the anterior part of the tail (11. p. 222).. 

 In others the caudal extension takes the form of an uusym- 

 metrical prolongation of the entire organ along the left side of 

 the tail, as in OpMocepJialus, or along the right side, as in the 

 Characinoid Alestes Sasselquistii, C. & V. {A. dentex, Miill. & 

 Trosch.) [11. p. 222] *, and in the Siluroids Gryptopterus micro- 

 oiema, Blkr., and G. onicropogon, Blkr. (2. pp. 202-3). More 

 frequently, perhaps, the air-bladder subdivides anteriorly to the 

 first caudal haemal arch, and in the form of two bilaterally- 

 arranged csecal prolongations extends for a variable distance on 

 either side of the tail and internal to the lateral caudal muscu- 

 lature, as in some Sparidse, Scombridse, and Carangidse (11. 

 pp. 221-2), and also as in Notopterus. But in none of the 

 Teleosts above mentioned, except Notopterus, or in any others with 

 which I am acquainted, do the caudal prolongations of the air- 

 bladder exhibit the slightest tendency to branch, or to develop 

 structures in any way comparable to the singular fringe of 

 bifurcate ventral diverticula which are so characteristic of 

 Notopterus horneensis ; and very rarely in anv Teleost are the 

 * On the authority of Cuv. & Val. 



