ACCOUNT OF A GANOID FISH FHOM QUEENSLAND. 
263 
lobate fins). Ceratodus clearly proves the correctness of this 
view, and we are fully justified in supposing that those extinct 
fishes with lobate fins had them provided with a similar internal 
skeleton. 
As in the other Gfanoid and Plagiostomous fishes, the heart of 
Ceratodus (fig. 4) is provided, in addition to the ordinary two 
divisions of the fish-heart, with a third contractile chamber, the 
conus arteriosus. The internal structure of the ventricle and 
atrium is extremely similar to that of Lepidosiren , but the val- 
vular arrangement in the interior of the conus arteriosus differs 
considerably, inasmuch as the valves are disposed in two or 
three transverse rows, of which, however, one only is fully 
developed. 
We have mentioned above that the Barramunda can breathe 
free air as well as air dissolved in water, and we may infer 
this from the perfect development of the gills and of a lung . 
There are four gills on each side ; they are broad, lamellated 
membranes, free from each other, but attached to the outer 
walls of the gill cavity, which peculiarity is clearly an approach 
to the fixed gills of the sharks and rays. The pneumatic ap- 
paratus may be described either as a single lung, with symme- 
trical arrangement of its interior, or as two lungs confluent into 
a single sac without a dividing longitudinal septum. Its in- 
terior is divided into about thirty compartments on each side, 
formed by strong transverse septa and cellular at the bottom ; 
it is evident that by this arrangement the respiratory surface 
is much increased in extent. This pulmonary sac extends from 
one end of the abdominal cavity to the other, and terminates 
anteriorly by a short duct in a glottis , viz. a slit with a valve 
in the ventral side of the oesophagus, somewhat to the right of 
the median line. In this respect the Barramunda shows itself 
to be a true fish, in spite of the presence of a lung, inasmuch 
as it is obliged to receive the air through the mouth, whilst 
nearly all Batrachians have the palate perforated by the nostrils, 
which form a distinct passage for the air used in breathing. 
When the fish sojourns in pure water, and breathes by the gills, 
the lung does not differ from the air bladder of other fishes ; 
it then receives arterial blood, returning venous blood, like all 
the other organs of the body ; but when the respiratory 
function rests with the lung, the pulmonary vein carries purely 
arterial blood to the heart, where it is mixed with venous blood 
and distributed to the various organs. 
Externally the intestinal tract appears as a wide straight sac 
without divisions or circumvolutions. Internally it is traversed 
throughout by a spiral valve performing nine gyrations ; the 
cavity before the commencement of the valve must be regarded 
as the stomach. The liver does not show any peculiarity. 
