416 Edward Phelps Allis jr., 



of the skull and that is wholly separate from the so-called premaxillaiy. 

 In both of my adnlt specimens this bone ison, the contrary, completely 

 and indistinguishably fused with the corresponding premaxillary. It 

 completely encloses, in the anterior two-thirds of its course, the inter- 

 trabecular cartilage of Parker's descriptions, here completely shutting 

 off both the vomer and the parasphenoid from direct contact with that 

 cartilage. A canal, enclosed in the anterior two thirds of the bone^ 

 gives passage to the olfactory nerve, which nerve leaves the bone on 

 its anterior aspect and passes immediately to the nasal capsule. 

 Parker's sections of larvae would seem to show that that part of the 

 bone that encloses the olfactory nerve is of purely membranous 

 origin, the bone of my adults thus containing an important membrane 

 component, as well as latero-sensory, and premaxillary tooth-bearing 

 ones. The homologue, in Amia and teleosts, of the membranous part 

 of this bone of Lepidosteus, I can not positively identify, but it 

 certainly is not either of the ethmoid bones, either primary or dermal, 

 of current descriptions of fishes. The only other bone in which it 

 could apparently find its homologue is the large posterior process of 

 the premaxillary bone of Amia, and this it seems to me to certainly 

 be. If this be so, Lepidosteus is to be added to Amia, the only other 

 fish in which this bone has heretofore been positively recognised, 

 though it is perhaps also found in Gj'^mnarchus [3, p. 454]. 



The preoperculo-mandibular canal arises from the main infraorbital 

 near the hind end of the squamosal, and iiinning downward immediately 

 enters the preoperculum which it traverses and then the mandible, 

 as shown in the figures, not anastomosing, at its anterior end, witli 

 its fellow of the opposite side. Near the dorsal end of the preoperculum 

 the trunk of a dendritic system arises from the canal, and running 

 upward and backward leaves the preoperculum and enters one or two 

 wholly independent, dermal, scale-like bones, in which it branches. 

 These latter bones lie immediately ventral to the lateral edge of the 

 squamosal, between the operculum and the outer corner of the sphenotic 

 (auto-postorbital) , which latter bone here comes to the level of the 

 outer surface of the dermal bones of the skull, considerably posterior to, 

 and out of all direct relations to the dermo-postfrontal. 



