418 Edward Phelps AUis jr., 



The main infraorbital canal first traverses several preorbital and 

 circumorbital bones, the homologies of which I have already elsewhere 

 discussed [6 and 7], and then enters and traverses the so-called post- 

 frontal, this latter bone being the dermo-postfrontal of Bridge's and 

 van Wijhe's nomenclature fused with an underlying auto-postfrontal 

 (postorbital ossification, AUis: sphenotic, Bridge). The superficial or 

 dermal part of this mixed bone lodges one sense organ of the main 

 infraorbital line, and has, to the adjoining bones, closely the relations 

 of the postfrontal of Amia. Posterior to this bone the canal traverses the 

 lateral, or squamosal portion of a parieto-dermosquamosal bone [5, p. 55], 

 that bone lodging two sense organs of the line, the anterior one innervated 

 by the ramus oticus and the posterior one quite probably by the 

 glossopharyngeus. Posterior to the squamosal the canal first traverses 

 the lateral one of three extrascapular bones, and then a suprascapular, 

 each of these two bones lodging a single sense organ of the line. 



The supratemporal canal begins in the latei'al one of the three 

 extrascapular bones, and traverses that bone and the two mesial ones, 

 each of the two latter bones lodging a single sense organ of the canal. 

 No organ of the commissure is found in the lateral extrascapular, 

 that bone only lodging one organ of the main infraorbital line. 



There are anterior and middle head lines of pit organs, but no 

 posterior head line. The anterior line has a position not strictly 

 comparable with that of the line in Amia. 



Neither Collinge nor Wright make any mention of a spiracular 

 latero-sensory organ in Polypterus, and my own dissections of the 

 fish were not carried deep enough to determine whether there is or 

 is not such an organ. 



Judging from Traquair's [7Ï\ and Pollard's [6Ï\ descriptions of 

 the skull, there is here, as in Lepidosteus, no temporal hole. 



Polypterus thus agrees with the other two living bony ganoids in 

 that the anterior end of the supraorbital canal is directed laterally 

 and backward between the two nasal apertures; and these three fishes 

 are the only ones in which this condition is known to exist. But in 

 Polyodon, Acipenser and Scaphirynchus, and hence probably in all the 

 cartilaginous ganoids, what is doubtless a strictly homologous arrange- 



