296 PROCEEDINGS OF THE CANADIAN INSTITUTE. 
trunk bear no ribs. The hemal 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 hemal arches firmly united 
below, but somewhat broadened so as to separate, as it were, the 
trunk and tail regions. The remaining hemal arches are exactly 
similar in appearance to the neural arches of their vertebra, possess- 
ing long spinous processes, certain of which assist in supporting the 
interspinalia of the anal fin. There is then in Amiwrus a gradual. 
passage from the transverse processes of the trunk region to the 
hzemal arches of the tail, and thus a strong argument in opposition 
to the view that the hzmal arches of the tail represent the trans- 
verse processes plus the ribs of the trunk. 
The typical features are present in all the vertebre posteriorly 
until one comes to the region of the eaudal fin (Pl. IL., fig. 5). Here 
some modifications occur. The neural and hemal 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 (H,) is somewhat expanded, and that of the third (#,) still 
more so, while that of the second (#,) 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 (,.) of these 
vertebre 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 
(N,) is not coalesced with their upper extremities, but forms a dis- 
tinct piece connected with them by ligament. The lower arch (H,) 
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 fossee above and below 
it, so characteristic of the other vertebre. 
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 vertebre in this terminal filament seems to be indicated by 
