296 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



trunk bear no ribs. The haemal arches of the last extend almost 

 directly downwards, parallel to each other, and are connected about 

 the middle of their length by a transverse bridge, above which runs 

 the aorta. The first tail vertebra has the haemal arches firmly united 

 below, but somewhat broadened so as to separate, as it were, the 

 trunk and tail regions. The remaining haemal arches are exactly 

 similar in appearance to the neural arches of their vertebrae, possess- 

 ing long spinous processes, certain of which assist in supporting the 

 interspinalia of the anal fin. There is then in Amiurus a gradual 

 passage from the transverse processes of the trunk region to the 

 haemal arches of the tail, and thus a strong argument in opposition 

 to the view that the haemal arches of the tail represent the trans- 

 verse processes plus the ribs of the trunk. 



The typical features are present in all the vertebrae posteriorly 

 until one comes to the region of the caudal fin (PI. II. , fig. 5). Here 

 some modifications occur. The neural and haemal processes of the 

 sixth vertebra (counting from the tail) are the first that are in rela- 

 tion to the caudal fin rays. They do not, however, suffer any modi- 

 fication, and are firmly coalesced with the centrum. So with the 

 arches of the fifth. The spinous process of the lower arch of the 

 fourth (ZT 4 ) is somewhat expanded, and that of the third (ff s ) still 

 more so, while that of the second (H 2 ) forms a very broad plate, 

 from the anterior border of which a thin plate extends to the poste- 

 rior edge of the third arch. The dorsal arches (iV 6 . 2 ) of these 

 vertebrae present no modifications. 



The last vertebra is, however, specially interesting. Its upper 

 arches, instead of projecting upwards and backwards, are directly 

 perpendicular to the axis of their centrum. The spinous process 

 (ffii) is not coalesced with their upper extremities, but forms a dis- 

 tinct piece connected with them by ligament. The lower arch (Si) 

 is fused with a small lateral process projecting from the lower portion 

 of the body, and expands to a broad plate in apposition with the 

 preceding and succeeding arch. The body is somewhat modified also, 

 wanting the lateral longitudinal ridge and the fossae above and below 

 it, so characteristic of the other vertebrae. 



The notochord extends upwardly and backwards from the last 

 vertebra almost at an angle of 45°. No further trace of centra are 

 to be perceived nor of dorsal arches, but the presence of several 

 coalesced vertebrae in this terminal filament seems to be indicated by 



