THE GANOID FISHES. 



21 



cutting and crushing. There is one pair of small teeth in the fore-part of the jaw which, from their 

 position upon a bone called the vomer, are termed vomerine teeth ; they meet each other at a right 

 angle, which is directed forward. The other teeth are much larger, and are crossed by six strong 

 ridges, which extend inward from the outer margin. Between these ridges are five notches. In a 

 specimen three feet long this tooth is an inch and a quarter long and half an inch wide. The cor- 

 responding teeth in the lower jaw have a similar shape, and are so placed as to fit against the 

 others and form an apparatus for grinding food. The hard parts of the fore-limb are entirely car- 

 tilawinous ; the paddle is joined to the scapular arch by a cartilage which represents the humerus. 

 A median row of cartilages of a quadrate form, twenty-six in number, extends the length of the 

 limb, and on both sides of it rays are given off which diverge downward and outward. This type of fin 

 is quite unparalleled, although the central series of cartilages may be compared to that of the Lepi- 

 dosiren. Dr. Giinther has compared the fin to the tail of an ordinary osseous fish ; nor is the plan 

 of structure very dissimilar to the tail of Ceratodus itself. The structure of the hind-limb is quite 

 like that of the fore-limb, except that it is rather more symmetrical and is shorter. The intestine 

 is neai-ly straight, and below the stomach is traversed throughout by a spiral valve, which may be 

 compared to that of Sharks and Rays, and winds around nine times. But the most remarkable 

 circumstance about this fish is the fact that it can breathe either by gills or by lungs, or simul- 

 taneously by both. The gills are not connected with spiracles, nor is there any true operculum. The 

 lung is single, and is a wide sac which extends down the middle of the dorsal region, from one end 

 of the abdominal cavity to the other. It is divided into about thirty compartments on each side, 

 and in these the tissue presents much of the character which is usually seen in the lung of a reptile. 

 It has a short duct terminating in a glottis, which opens on the ventral side of the gullet. The air is 

 probably expelled from the lungs much as among reptiles by the tissue contracting ; and this is 

 thought to account for the grunting noise heard at night when the fish are out of water. The 

 species has been named Ceratodus forsteri. 



CEUATODVS. (After Gimlher.) 



ORDER II. GANOIDEI, OR FISHES WITH BONY SCALES. 

 FAMILY I. AMIID^E. THE NORTH AMERICAN MUD-FISH. 



The Ganoid fishes are a group fast verging on extinction, and are represented at the present 

 day by three families, which include four genera and six species ; but from the light which their 

 structure throws on the fossil forms of both Primary and Secondary strata, no less than from some 

 remarkable points of structure, they deserve notice. In the first family, Amiidse, there is but one 

 species Amia calva, which is known as the Bow-fin of Lake Champlain, the Dog-fish of Lake 

 Erie, the Mai-sh-tish of Canada, and is sometimes known as the Mud-fish. The body is long, com- 

 pressed behind, and sub-cylindrical. The head is broad, with a short snout ; the jaws are margined 

 with an outer series of delicate sharp-pointed teeth, which are closely set, and there are patches ot 

 similar teeth on the vomer, palatine, and pterygoid bones. The lower jaw has a single row of 



