THE OSTEOLOGY OF AMIURUS CATUS. 297 
the presence of several hemal arches. Of these there are in all six, 
the four lying immediately below the ternunal filament of the noto- 
chord being separated from the other two by a distinct interval, cor- 
responding to the longitudinal axis of the body. The lowest (A) 
(z.e., the one posterior to that of the last vertebral centrum) is fused 
with the posterior inferior portion of the last vertebral centrum, and 
bears at its base a slight lateral ridge. It expands very much towards 
its extremity, being the broadest of all these fin-bearing arches, 
The next four (4, C, D & LH) arise from the posterior surface of the 
last centrum, being fused with it. They are triangular in shape, 
expanding posteriorly, and diminishing in size from below upwards. 
The last (/’) (7.e., that unmediately below the notochord) is small, 
and partly enclosed by the lateral bones enclosing the notochord. It 
seems to arise from these structures near their base. 
We have thus six hemal arches which are well developed, and 
specially modified for the purpose of supporting the rays of the 
caudal fin, the centra and upper arches corresponding to them having 
become aborted, or perhaps the centra are represented by the last 
body, several having fused to form it. Lotz’ has investigated the 
structure of these vertebre in Cyprinoids and other fishes, and in 
the former there appears to be an arrangement very similar to that 
of Amiwrus. The specialization however does not seem to have pro- 
gressed quite so far. In Sarbus the third or second vertebra bears 
two dorsal arches. The spinous process of the last dorsal arch is 
similar to that of Amiwrus, Lotz naming the free spinous process a 
‘falsche Dorn,’ believing it to be either a part of the true spinous 
process or a free fin-bearer. I prefer the former hypothesis. The 
three lower arches, which have no distinct vertebrae, are fused with 
the last centrum, as in Amiwrus, but the upper four are independent. 
It would appear from this that the last vertebral centrum really 
consists of three fused centra, those of the four upper hemal arches 
having become aborted, the fusion of these arches with the last 
centrum in Amiwrus being secondary. All these lower arches are 
tipped with cartilage, but there are no intervening cartilaginous 
pieces as in Barbus. 
Extending back from the posterior superior angles of the last cen- 
trum on either side of the notochord filament are two bones (1S) 
1 Lotz.—Ueber den Bau der Schwanzwirbelsaule der Salmoniden, Cyprinoiden, Percoiden 
und Cataphiacten. Zeit. f. wiss. Zool, XIV., 1864 
