430 Edward Phelps Allis jr., 



sphenotic (postorbital ossification) and not the postfrontal bone. 

 Leaving this bone the canal traverses the parieto-sqamoso-epiotic of 

 Huxley, the squamosal of Pollard, that bone lodging three sense organs 

 and being the exact homologue of the squamoso-extrascapular of the 

 other siluroids above discussed. 



Pollard's statement that certain primary tubes in this fish and in 

 Auchenaspis must be regarded as rudimentary canals representing 

 certain of the pit lines of Amia, has already been referred to by me, 

 in an earlier work, as too evidently erroneous; and needs no further 

 comment. 



Trichomyderus and CaUichthys. In both of these fishes the 

 supraorbital canal seems, from Pollard's descriptions, to anastomose 

 with the main infraorbital by its terminal primary tube, as it does 

 in Lepidosteus, instead of by a penultimate tube, as in Amia and in 

 the other siluroids already discussed. 



In Trichomycterus, the postfrontal organ is the most anterior 

 one of the main, posterior portion of the main infraorbital canal, the 

 more anterior portion of this infraorbital line being represented only 

 by a short antorbital canal that lodges a single sense organ. Be- 

 tween these two sections of canal Pollard could find no sense organs, 

 but as he failed to find any lines of pit organs in any of the several 

 fishes examined by him, it is probable that a certain number of 

 organs, belonging to the infraorbital line, here existed as pit organs, 

 but were overlooked. The condition of the canal itself, as shown by 

 Pollard, is important, as affording further proof that the postfrontal 

 organ belongs to the squamosal rather than to the infraorbital portion 

 of the canal. The relations of most of the sense organs to the dermal 

 bones are not at all definitely given. 



Characinidae. 

 Macrudon trahira. The main infi'aorbital canal, in Macrodon 

 (figs. 11 and 12), begins anteriorly at a pore that lies dorso-mesial 

 to til e posterior nasal aperture, slightly anterior to the anterior edge 

 of the eye. From there the canal runs downward and backward 

 posterior to the posterior nasal aperture, between it and the eye, thus 



