On certain features of the lateral canals and cranial bones of Polyodon folium. 673 



nasal is "apparently" represented in his bone C\ This latter bone 

 thus certainly not being a piscine nasal bone is probably a "dermal 

 ect-ethmoid", a possibility that Bridge suggests though treating it as 

 improbable. 



The hyomandibular canal, on both [sides of all of my several 

 specimens, arises from the main infraorbital canal anterior to the 

 point of anastomosis of that canal with the supraorbital canal. Col- 

 LiNGE shows this canal, in all of his several figures, arising posterior 

 to that point, apparently from the main infraorbital canal as it tra- 

 verses my bone 1. This is such an important difference that it seems 

 to me that Collinge must here be in error, for the canal arising, as 

 it does in my specimens, from the postorbital portion of the main 

 infraorbital has an origin comparable with that of the similarly named 

 canal in selachians ; while arising, as Collinge shows it, from the 

 squamosal portion of the main infraorbital canal, and yet anterior to 

 the spiracle, it would have an origin and position totally different 

 from that of any known canal in other fishes. From its point of 

 origin in my specimens it runs downward and backward antero-ventral 

 to the spiracle, and then has the general course that Collinge gives. 

 The mandibular portion of the canal ends, however, in a definite 

 terminal tube opening by a single pore, instead of gradually diminishing 

 in size and vanishing in a point, as Collinge shows it. There are 

 also, in all my specimens, several primary tubes given off in this 

 mandibular portion of the canal, most of them being short and simple 

 tubes opening by a single surface pore. There is no slightest in- 

 dication, in any of my specimens, of the maxillary branch shown and 

 described by Collinge. There are also no primary tubes, in two of 

 my specimens, and but one in another, on the anterior side of the 

 hyomandibular part of the canal, a place where Collinge shows four 

 large dendritic systems. Certain of the branches of the dendritic 

 systems of this part of the canal, in my specimens, as in Collinge's, 

 open by pores that are in marked proximity to the pit-like organs of 

 the region, Collinge's primitive pores, but the relation is certainly 

 one of proximity only. The canal is everywhere enclosed, or partly 

 enclosed, in delicate bones, these bones, in the hyomandibular region, 

 lying in the skin superficial to the hyomandibular; while in the 

 mandibular region they lie, in the posterior part of the length of the 

 canal, superficial to the interhyal and ceratohyal of Bridge's de- 

 scriptions, and, in the anterior part of the length of the canal, between 

 the latter element and the mandible. In no part of their course do 



