524 PBOr. T. W. BKIDGE OlST THE 



median line. On the otTier hand, however, Notopterus differs 

 from the more typical Siluroids in the absence of the transverse 

 septum on the right side, the unsymmefcrical division of the air- 

 bladder by the longitudinal septum, and also in the fact that it 

 is the basioccipital which is carinate ventrally and not, as in 

 Siluroids, the confluent centra of the " complex " vertebra. 



An additional resemblance to many Siluroids is also apparent 

 in the tendency of the outer fibrous coat of the air-bladder to 

 become invaded by ossific deposit whenever it becomes attached 

 to, or inserted into, adjacent portions of the axial skeleton. The 

 bony ridges which bound the basioccipital grooves for the 

 reception of the auditory caeca, and the squamous hinder portions 

 of the prootiss which form the outer walls of the bony culs-de~sae 

 wherein these caeca terminate, almost certainly owe their existence 

 to the ossification of the tunica externa at the points where it is 

 attached to these cranial bones. 



By no means the least notewortliy of the many interesting 

 structural features in connection with the air-bladder of Noto- 

 pterus iorneensis is the extreme shortness and relatively wide 

 calibre of the ductus pneumaticus, and the position of its oeso- 

 phageal aperture in close proximity to the last pair of branchial 

 clefts. Such a combination of features is eminently charac- 

 teristic of the Acipenseroid, Crossopterygian, Amioid and 

 Lepidosteoid Teleostomi and of the Dipnoi, but is rarely to be 

 found in Teleosts, although an approximation thereto may be 

 noted in such genera as Arapaima, Seterotis, and Gymnarchus, 

 at any rate to the extent that in these Teleostei the ductus is 

 both short and wide. 



In the absence of gas-secreting or gas-absorbing " red glands" 

 and " red bodies," Notopterus agrees with the generality of those 

 Teleosts in which an open ductus pneumaticus is retained 

 throughout life. 



From a physiological point of view, the most noteworthy 

 feature in the air-bladder of Notopterus is its intimate relation 

 with the auditory organ. 



The presence of antero-lateral caecal outgrowths from the air- 

 bladder is by no means uncommon in Teleostean Fishes, especi- 

 ally in the Sparidse, Scisenidse, Cottidse, and Gradidae ; and such 

 outgrowths may even extend so far forwards as to become more 

 or less closely related to the skull, but it is only in a compara- 

 tively limited number of genera that the air-bladder acquires any 



