The Latero-Sensory Canals and Related Bones in Fishes. 491 



both Eurysomus and Wardichthys, that the supraclavicular is perforated 

 by the lateral line canal. This latter statement would also seem to 

 indicate that the cranial latero-sensory canals were, in both these 

 families of fishes, wholly enclosed in the cranial bones, and not there 

 simply represented by open grooves; but Traquair's figures of Nemato- 

 ptychius seem to show them as simple grooves. The supraorbital 

 canal of this latter fish is shown beginning near the centre of the 

 parietal and fiora there running forward across the frontal and then 

 the prefrontal, at the anterior end of which latter bone the canal lies 

 lateral to the nasal aperture. The canal does not apparently anasto- 

 mose with a main infraorbital canal, this latter canal not being shown, 

 and its position, lateral to the nasal aperture, is unknown in living 

 fishes, in so far as my experience goes. The only possible suggestion 

 of an homology here seems to be that the so-called prefrontal of this 

 fish is an antorbital bone, similar to that bone of Lepidosteus, and 

 that the canal it lodges is the upper anterior end of the suborbital 

 part of the main infraorbital canal, and not the anterior end of the 

 main supraorbital canal. 



In Macropetalichthys the latero-sensory canals were probably also 

 wholly enclosed in the bony elements of the cranial shield, for Cope 

 [5i, p. 450] says that the double suturai lines of Newberry's descriptions 

 of this fish are "tubes"; an observation confirmed by Dean's statement 

 [34, p. 115J that, in this fish, "The mucous system often appears as a 

 series of open canals, as in the Arthrodira; in favourable specimens, 

 however, each canal is shown to be covered by a delicate roof, per- 

 forated by two lines of minute openings". This double row of pores 

 along each canal is a peculiarity also of the Pteraspidae, and of those 

 fishes alone of all others that I find described. It is certainly not a 

 chondrostean characteristic, and yet it is with the chondrosteans that 

 Macropetalichthys is classed by Zittel, 



In no other fossil ganoid or dipnoid can I find, in the literature 

 at my disposal, any description of a latero-sensory canal enclosed in 

 any of the cranial or shoulder bones; nor do I find any descriptions 

 of pores, on the outer surface of the cranial bones, that could with 

 any certainly be taken to be the surface openings of those canals. In 



