126 EDWARD PHELPS ALLIS, .TUN. 



latter fish being, in that case, the exact homologue of the pre- 

 opercular canal line of Amia. 



One feature of this hyo mandibular canal of selachians is 

 worthy of notice, though just what its morphological signifi- 

 cance may be I cannot tell. The so-called proximal end of 

 the canal, that is, the end at which it anastomoses with the 

 infra-orbital canal, leaves, or joins, that canal anterior to the 

 spiracle, while the nerve that innervates it descends posterior 

 to the spiracular canal. This relation of the canal to the 

 spiracle is much more marked in Polyodon (13, figs. 3 and 

 12), in which fish the branches destined to innervate the 

 organs in the dorsal part of the canal, if there be any, must, 

 to reach the oi"gans, curve forward and upward ai'ound tlie 

 ventral surface of the spiracular cleft. This relation is a 

 singular one, and seems to call for some special explanation, 

 which may, perhaps, be found in the assumption that a part 

 of the line is represented in the horizontal cheek line of 

 pit organs of Amia. In Polypterus (6) the dorsal end of 

 the pre-opercular canal lies at the hind end of the spiracle, 

 in what would seem to be its natural relation to that 

 opening. 



In Chlamydoselachus (21) there is a very close general 

 agreement of nearly all the canal lines with the lines in the 

 projection of Mustelus. The so-called occipital canal of 

 Garman's descriptions of the former fish is the otic canal of 

 my descriptions of the latter. The aural of the former fish 

 is probably represented in Mustelus, as already stated, by the 

 two supratemporal pit organs. The orbital, suborbital, and 

 orbito-nasal canals of Chlamydoselachus are the postorbital 

 and suborbital parts of the infra-orbital canal of Mustelus. 

 The nasal and prenasal of Chlamydoselachus, including 

 between them the region of the non-existent median, are the 

 "dntorbital section of the infra-orbital of Mustelus. The sub- 

 rostral, rostral, and cranial of Chlamydoselachus are the 

 supra-orbital of Mustelus. The angular of Chlamydoselachus 

 is the hyomandibular of Mustelus, and the jugal, oral, 

 spiracular, and gular of Chlamydoselachus are, together, 



