386 



Vertehrata. 



ventral to the long, bent-up poi-tion of the spinal column (Fig. 299 B). Rhom- 

 boidal scales. Several species in N. America. 



3. Amia. Externally almost exactly like a Teleostean ; it has cycloid 

 scales. For its chief characteristics see p. 375, foot-note * : p. 377, foot-note * ; 

 Fig. 304 C ; Fig. 310 B. It occui-s in North America. 



Order 4. Dipnoi. 



TKe skeleton is partially ossified; the conus arteriosus spirally 

 coiled and provided inside with a longitudinal fold formed of 

 modified valves ; a spiral valve in the intestine ; the operculum is 

 supported by bony plates ; the lung is functional ; the skin 

 provided with scales, the fins with unsegmented, soft, bony rays. 

 Both anterior and posterior nares lie within the mouth. The limbs 

 are either long, pointed plates, with a median, segmented, cartila- 

 ginous rod, from either side of which a series of cartilaginous rays 

 arise ; or they are filiform, with a similar, but more or less reduced 

 skeleton. The tail is pointed and diphycercal ; notochord uncon- 

 stricted and well-developed ; a few large teeth in the mouth. 

 Exclusively freshwater. 



This aberrant group, which at the present day is represented by a few forms 

 only, is most nearly allied to the Ganoids, especially the Holostei. The structure 

 of the conus is remai-kable, recalling the condition in the Amphibia {q.i}.) ; in 

 connection with it are certain peculiarities in the structure of other parts of the 

 heart, by which a partial separation of blood from the lung and from the rest 

 of the body is effected. The structure of the limbs, the position of the nares, 

 etc., is also very peculiar. 



Fig. 316. Ceratodus.- After Giinther. 



1. The Mud-fish or Barramunda (Ceratodus) is a large, elongate 

 animal, pointed at both ends ; with large scales ; large, broad limbs ; dorsal, 

 caudal and anal fins continuous. It inhabits the rivers of Australia. 



Fig. 317. Protopterus annectens. 



