ORDERS OF FISHES. 167 



plates of the lower jaw correspond to the upper, their un- 

 dulated surface fitting exactly to that of the opposite teeth. 

 Besides these molars, the front part of the upper jaw 

 (vomer) is armed with two obliquely - placed incisor - like 

 dental lamellae, which have no corresponding teeth in the 

 lower jaw. As we know the kind of food taken by the 

 Barramunda, the use of these teeth is apparent. The incisors 

 will assist in taking up or even tearing off leaves, which are 

 then partially crushed between the undulated surfaces of the 

 molars. 



" The skeleton consists of a cartilaginous basis, in the form 

 of a long tapering chord for the body and tail, and in that 

 of a capsule for the head. No segmentation into separate 

 vertebr£e is visible in any part of the notochord ; but it sup- 

 ports a considerable number of apophyses, the abdominal of 

 which bear well-developed ribs, all being solid cartilaginous 

 rods, with a thin sheath of bone. In the same manner no 

 part of the brain-capsule is ossified, but it is nearly entirely 

 enclosed in thin bony lamellcTe. This is also the structure of 

 the appendages of the skull, as the mandible and the hyoid 

 and scapulary arches. From a study of the skull, it becomes 

 apparent at once why in fossil teeth of Ceratodus nothing or 

 very little of the bone attached to them has been preserved. 

 These teeth rest on cartilage as well as on bone, the latter 

 being a very thin and porous layer which could not be pre- 

 served, unless the progress of stratification had been going 

 on with as little disturbance as in the Solenhofen Schiefer ; 

 but the matrix in which fossil Ceratodout teeth are found 

 shows that it was formed under very different conditions, 

 and it is certainly not of a nature to permit the supposition 

 that thin porous lamellse of bone would have been preserved 

 entire. 



" The structure of the skeleton reminds us much of that 

 of the Sturgeons, Chimsera, and especially of Lepidosiren ; 

 and of all the modifications by which it differs from these 

 types, perhaps none is of greater interest than that observed 

 in the paddles. The central part of the paddle, w^hich we 

 have found externally to be covered with scales, is supported 

 by a jointed axis of cartilage extending from the root to the 



