ON THE ANATOMY OE FISHES. 
121 
Pimelodus pidcher, Boul. 
Our exaiiiples of this species formed part of the collection of Fishes made by the 
late Mr. Clarence Buckley, at Canelos, in Western Ecuador, and subsequently 
described by Mr. G. A. Boulenger in the ‘ Proc. Zool. Soc. of London,’ for 1887, 
p. 274. As both the air-bladder and certain portions of the skeleton exhibit some 
interesting deviations from the normal type, a more detailed notice of this species will 
be given. 
The first, the complex, and the fifth vertebrm are more or less rigidly connected 
together by the usual means, the sixth being the first that is freely moveable (fig. 3‘J, 
V.', C.C., v}, and r.®). The body of the first vertebra is very small. The complex 
centrum is nearly twice the length of the fifth centrum, and this again is somewhat 
larger than any that follow. The ventro-lateral edges of the complex and fifth centra 
are thickened by a continuous deposit of superficial bone, which, however, does not 
extend ventrally or laterally so as to convert the grooves for the dorsal aorta {a.g.) 
and posteiior cardinal veins into complete bony canals. The cardinal grooves are 
rather deep and, as usual, that on thr right side is more conspicuous than the left one. 
Badial nodules are attached to the lateral surfaces of the complex centrum, and from 
each nodule a slender dorsal lamina {dd.) is continued obliquely backwards and 
upwards, ventrad to the corresponding cardinal groove, along the posterior margin of 
the transverse process of the fourth vertebra, with which the lamina eventually 
fuses. 
The expanded transverse processes of the fourth vertebra {tpd) have broad fiat 
roots, but are strongly decurved along their anterior margins and produced distally 
into slender recurved processes, which form the inner walls of the sockets for the 
clavicles ; to the decurved anterior margin of each process the inferior limb of the 
post-temporal {pt.i.) is closely applied. The jDosterior portion of tlie process is nearly 
flat, but terminates distally in a pointed projection. The ventral surface of each 
transverse proce.ss will therefore form a shallow, transversely-disposed recess, which is 
slightly concave from before backwards, except for a short distance at its root. TTie 
transverse process of the fifth vertebra (tpd) is quite free, and much longer than the 
normal rib-bearing processes. 
The air-bladder is partially constricted into two ovoid, laterally-situated sacs (figs. 
39 and 40, a.s.), which occupy the concave recesses furnished by the modified trans- 
verse processes of the fourth vertebra {t.pda.), and are in free communication witli 
each other through a narrow tubular portion passing from one to the other across the 
ventral surface of the complex centrum.'" This intermediate tubular portion is 
connected by a persistent ductus pneumaticus with the oesophagus. There is no 
trace of lateral compartments. As regards its rigid skeletal attachments and the 
* Jn a specimen three inches long the autcro-posteriur extent of each sac was 3 o min., and the trau.s- 
verse 4 mm. 
.MDCCCXCIII. — 15. 
U 
