Gunther—LP linthophorus robustus. el 7 
the caudal portion are preserved. Both ventral series, that of the right 
side as well as of the left, are visible, and in their natural connection ; 
that of the left side, however, has been somewhat displaced, and the 
inner surface of its scutes became exposed to view. ‘This series runs 
from behind the root of the pectoral fin to the outer ventral ray ; it 
is continued behind the ventrals, but only a few of the scutes of this 
sub-caudal portion are preserved, two presenting their outer surface, 
and three their inner. All these are before the anal fin, and it is 
doubtful whether the series was continued beyond it. 
The general form of these scutes is arrow-head-shaped, with a 
longitudinal keel running from one end to the other; the uncovered 
broader posterior part is corrugated; the anterior portion, which is 
covered by the preceding scute, is more slender, tapering, and smooth. 
All these scutes were so connected that they could easily slide one 
above the other, allowing the lateral motions and the temporary ex- 
tension of the body after feeding or during the season of propagation ; 
and the whole arrangement reminds us of a similar chain of scutes in 
Doras and Hypostomus. Their inner surface is smooth, with a longi- 
tudinal groove on the posterior half, to receive the keel of the scute 
next following. Those of the anterior part of the dorsal series are the 
largest, and comparatively short, being only six lines long and five 
lines broad; only a small part of them is covered by the preceding 
shield, as no great mobility was required in this part of the fish. 
Posteriorly they become rather smaller and narrower. ‘The scutes 
of the abdominal series are much narrower, and from six to seven 
lines long ; their corrugated posterior portion is much shorter than 
the anterior smooth part, and there is a very distinct flat prominence 
on each side where the corrugated part passes into the smooth sur- 
face. The scute at the base of the ventral fin is especially large, 
differing in shape from the others ; the upper half of its posterior 
portion, which is on the side of the trunk, is produced backwards, 
whilst the lower half is, as it were, cut off, to allow the insertion of 
the ventral fin; the entire length of this scute is one inch. ‘The 
scutes behind the ventral fin are the smallest of the series, sub- 
rhombic, 44 lines long and 38 lines broad. 
Although it is probable that Plinthophorus must be placed 
near to Rhinellus, the degree of their aflinity cannot be ascer- 
tained before the structure of its head, and especially of its 
jaws, is known. ‘The difference in the series of osseous scutes 
appears to justify, at present, its generic distinction. As regards 
the position of these genera in the system, no ichthyologist of 
the present day will maintain their aftinity to the Sclerodermata, 
to which they have been referred by Agassiz. They belong 
even to a different family than Dercetis, as is clearly shown 
by the form of the vertical fins. Whether these fishes be 
Ganoidei or Teleostei cannot be decided in the present state of 
our knowledge; but if they should belong to the latter subclass, 
they are the remains of an extinct family, not represented in 
