788 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [42] 



as haviDg been derived through progressive development from existing 

 structures in the Selachii. 



To these belong the diverse courses of the ramus palatinus in the 

 Selachians and in the higher fishes, the relations of which cannot be 

 directly derived from one another. Yet it is not improbable that in 

 this case we are dealing with a substitution of very different and appre- 

 ciable nerve branches, as often happens in fishes. 



In most of the plans of structure in theshull of Amia a direct progress 

 in development can he discerned in parts from those that already exist in 

 Selachii ; and it is particularly the Notidanides — the least differentiated 

 of the Selachians — which present the most evident relations to Amia for 

 recognition. 



It would be very difficult to specify the distinguishing characters be- 

 tween the cranium of Atnia and that of the Teleostei. There are but very 

 few characteristics to be found in the skull of Amia that could not be 

 found in one or the other of the families of the Teleostei, and these 

 few distinguishing characters are not restricted to Amia, but are also 

 found in other Ganoids. In this category belongs the continuate, non- 

 fenestrated, cartilaginous cover of the primoidal skull, in which, among 

 the Teleostei, vacuities are always discoverable, but it has preserved 

 its integrity in the Accipenserides among the Ganoids. A second im- 

 portant distinction is the absence of the supraoccipital in A^nia and all 

 the other Ganoids, while in the Teleostei it occurs quite constantly. 

 The third distinction— already described above — refers to the course of 

 the olfactory nerve in a direct prolongation of the brain case — is shared 

 by Amia with all the other Ganoids. 



Postscript. — Just as this article had passed into the hands of the 

 printer, I received a copy of the treatise by J. Van Wijhe, " Upon the 

 visceral skeleton and the nerves of the Ganoids " (JSTetherlands Arch, 

 f. Zoolog., Vol. v.. Part III, 1882), in which the cranial nerves of 

 Amia are described. I am glad that Van Wijhe agrees with me in all 

 the essential points. I must also state that Van Wijhe has invited 

 attention to the importance ' of the mucus canals in determining the 

 bones that overlay the skull (L c, page 228).^'^ 



4^ Dr. Sagemliel's paper is completed by a rSsiim^ of the lettering of the figures, or 

 an " Explanation of figures in the plate," hut I have omitted this, as the figures are 

 separately described in their appropriate places here. — Trans. 



