278 



vomer, the premaxillaries of Polypterus then having palatal processes 

 developed independent of the vomer bones. But as the subrostral and 

 the palatine processes of the premaxillaries were apparently fused in 

 Traquair's specimen this is perhaps not an important distinction, even 

 if true. Further work must decide the question. 



The two or one subrostals, and the paired vomers, of Polypterus, 

 are thus, none of them, probably represented by bones in Amia, but 

 whether they are so represented in certain Teleosts, or not, I am un- 

 able to judge from the works at my disposal. They may be the homo- 

 logues of the "accessory palatine" described by Sagemehl (No, 37, 

 p. 95) in Macrodon, and they must have some relation to the little 

 blocks of cartilage, or procartilage, said by Pollard (No. 33) to be 

 found in the maxillary velum of the young of certain Siluroids, and 

 also of many other Teleosts. These little cartilages would then per- 

 haps have their homologues in the cartilaginous blocks found in the 

 barbels of Acipenser, the barbels themselves being special modifications 

 of the breathing valve. 



In Amia there is, as stated above, no mandibular breathing valve. 

 There are, however, in this fish, as in Polypterus, certain presplenial, 

 tooth- bearing dermal plates, but they do not have the horizontal po- 

 sition of the plates of Polypterus, and there is no indication whatever 

 of a mucous fold related to them. They must, nevertheless, represent 

 the mandibular valve of the fish, being, as they are, so unquestionably 

 the homologues of the bones of Polypterus. The mandibular valve has 

 simply here either become completely coalesced with the underlying 

 tissues, or Amia represents a stage before the appearance of the fold 

 as a valve. 



The maxillary breathing valve of Teleosts has its attachment some- 

 times to the inner surface of the premaxillary bone alone, and some- 

 times to the inner surface of that bone and also that of the maxillary. 

 It thus, in these latter fishes, lies wholly external to the pterygopalatine 

 line of bones. In Polypterus, on the contrary, its posterior portions 

 must lie internal to that line if the so-called vomers of the fish are 

 ossifications of the valve. This diff"erence of position does not, however, 

 seem to me sufficiently important to seriously atfect the homologies I 

 have proposed. It may even be found that the so-called maxillary 

 bones of certain Teleosts are not those bones at all, or that they are 

 formed by the fusion of the maxillary bones with the dermopalatines. 

 Thus, in Conger conger, the so-called maxillary bone certainly con- 

 tains the dermopalatine, but whether this latter bone is fused with 

 the maxillary or with the premaxillary of the fish I should hesitate to 



