Wellington Philosophical Society. • 491 



ciently pure to yield the necessary supply of oxygen, the function ol 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 vertebra?, and with only a simple capsule for a brain case. 

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



lim 



j aws for the attachment of the teeth, are slightly rigid . 

 The limbs are two pairs of paddles, very similar t 



fins of fishes, resembling more the appearance 



of the paddles of an Ichthyosaurus. 



The 



point 



palaeontologist 



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 ot 

 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 



them 



Museum, bein 



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



expedition. 



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



barrier. 



that were exhibited had been taken. An 



in 



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. 



been 



soundin 



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 



Sydney to Cook Strait. 



ian 



soundings 



