Wellington Philosophical Society. 491 



ciently pure to yield tlie necessary supply of oxygen, the function of breathing 

 rests with the gills alone j but when the fish is compelled to sojourn in thick 

 muddy water charged with noxious gases, which must be the case very 

 frequently during the droughts which annually exhaust the creeks of tropical 

 Australia, it commences to breathe air by its lung direct from the atmo^ 

 sphere, rising to the surface of the water from time to time for this purpose. 



The skeleton of the Barramunda, and the construction of its heart, require 

 it to be placed, as Dr. Giinther has shown, among the ganoid fishes — • 

 a section of the cartilaginous fishes that was largely developed in early 

 geological times. Notwithstanding its large size and well-developed fins, its 

 internal skeleton is only represented by a long, tapering, cartilaginous cord, 

 without distinct vertebrae, and with only a simple capsule for a brain case. 

 The appendages of this central structure are, however, encased in a thin crust 

 of bone, so that the ribs and processes for the attachment of the limbs, and the 

 jaws for the attachment of the teeth, are slightly rigid. 



The limbs are two pairs of paddles, very similar to each other in shape, 

 and very unlike the ordinary fins of fishes, resembling more the appearance 

 of the paddles of an Ichthyosaurus. The teeth of the Barramunda consist of 

 hard plates, four above and two beneath, and they afibrd the chief point of 

 interest which this remarkable fish possesses for the palaeontologist, as they 

 exactly resemble the fossil teeth described under the name of Ceratodus. It 

 is now easily understood why nothing but the teeth and the ganoid scales ol 

 the extinct fish should have been preserved. A few specimens of the Barra- 

 munda were obtained by Professor Wyville Thomson on his recent visit to 

 Queensland, while H.M.S. *' Challenger" was in Sydney, and among them 

 this specimen, which he brought specially for this Museum, being one of the 

 most important of the many contributions we received from the " Challenger" 

 expedition. 



The " Challenger," after leaving the Cape of Good Hope, went as far south 

 as 67°, close to the ice barrier, and visited Kerguelen Land, where some 

 interesting photographic views that were exhibited had been taken. An 

 interesting point, illustrated by microscopic specimens on the table, is that at 

 a depth of 2600 fathoms, close to the ice, the sea-bottom is composed of 

 siliceous Diatoms, while in the same depth further north the deposit is formed 

 of calcareous Foraminifera. The latter appear to have been dissolved in the 

 cold polar under-current, so that when they are reached in the deep soundings 

 in more temperate latitudes only a fine mud is found, composed of the small 

 percentage of insoluble matter which the calcareous skeletons contain. In 

 taking soundings for the telegraph cable line, the '' Challenger" ran a straight 

 course from Sydney to Cook Strait. On leaving the Australian coast the 

 soundings showed a gentle gradient to the great depth of 2600 fathoms, which. 



