[41] THE OSTEOLOGY OF AMIA CALVA. 787 



At this point I would remark, that in the matter of position of the 

 hyomandibular articulation, it is the Notidauides among all the Sela- 

 chians, that still most resembles Amia aud the Teleostei. 



The parietal grooves which occur in the skull cover of many Sela- 

 chians, and which include the broad, blind terminal parts of the aquae- 

 ducti vestibuli, are missing in all the Ganoids and Teleosteaus. This 

 has evidently something to do with the very imperfect development of 

 the aquseducti in the higher fishes as compared with that structure in 

 the Selachii. 



At the base of the primoidal skull we invariably find in higher fishes 

 a fenestration in the region of the hypophysis cerebri that is lacking 

 in the Selachii. 



Postorbital and antorbital processes occur in most of the Selachii as 

 well as in Amia and most all the Teleostei. 



The optic foramen of the Selachii— already exhibiting evidences of 

 increasing size — is represented in the orbital region of Amia by an ex- 

 tensive vacuity. 



The cartilaginous peduncle which supports the eye in many Selach- 

 ians, is in Amia reduced to a fibrous cord. Only the merest traces exist 

 in the orbits of Amia of that basal projecting ledge of the primoidal 

 cranium and the vault as they occur in the Selachii. 



The very characteristic vacuity which occurs in the prefrontal cover- 

 bone of the primoidal skull in the Selachii is wanting in Amia, but ap- 

 pears to be present in certain families of osseous fishes, in Cyprinoida 

 and Oharacinids. 



Kot a few differences in the structure of the nasal region between the 

 Selachii and the higher fishes, including Amia, can be made out. 

 While the nasal apertures in the Selachians are situated upon the lower 

 aspect of the snout, in higher fishes they are without exception on the 

 lateral or upper plain of the head; besides, the well-developed nasal 

 capsules of the Selachii are reduced to quite flat pits in Amia and in 

 the bony fishes. 



A structure homologous with the nasal alar cartilage of the Sela- 

 chians is entirely wanting in Amia, but can be pointed out, as demon- 

 strated above, in certain bony fishes. 



Still another, not unimportant, difference in the structure of the nasal 

 region in the higher fishes and that of the Selachians is to be recognized 

 in the fact, that in the former articular facettes for articulation with the 

 anterior end of the palatine arch are developed on the inferior aspect 

 of the region referred to. 



The characteristic interrupted rostra, occurring in many Selachians, 

 are wanting in the higher fishes, either entirely or are replaced by sim- 

 ple uninterrupted structures, that approach in this respect the rostra 

 of the Notidanides. 



The recapitulation of our investigations go to prove that there are 

 several structures in the organization of Amia that, cannot be regarded 



