154 EEPORT OF STATE GEOLOGIST. 



fifth gill-arch are present in fishes, but they bear no gills. It consists on- 

 each side of a single enlarged bone, the lower pharyngeal, which nearly 

 always carries teeth. The upper ends of some of the other arches form 

 the upper pharyngeals, also tooth bearing, and these two sets of teeth 

 work against each other in triturating the food. In the suckers and 

 minnows the lower pharyngeals are scythe-shaped and carry a few large 

 teeth. 



Between the gills are the gill-slits, passages through which the water 

 issues from the pharynx. Often the slit behind the fourth gill is reduced 

 to a mere pore, and it may be wholly closed. The external gill opening 

 is usually large, but maybe reduced in size. In the eel the openings are 

 small and close together. In the paddle-fish and the sturgeon there is 

 found on the top of the head a pore, the spiracle. This is the external 

 opening of a tube which internally communicates with the pharynx. In 

 a large number of fishes there is a small, gill-like organ, the pseudo- 

 branchia, to be found on the inner side of the gill-cover and near its up- 

 per border. It is present in the yellow-perch and the jack-salmon (Sti- 

 zostedion). In the bass and the sun-fishes it is covered with the skin so as 

 to be somewhat concealed. 



As already stated, teeth may occur on the premaxillaries, maxillaries, 

 vomers, palatines, pterygoid.^, dentaries and the pharyngeals. They may 

 also be found sometimes on the bone at the base of the skull, on the 

 tongue, and on the gill-arches. The teeth vary greatly in form and size. 

 When fine and close-set and in bands, they are said to be villiform ; when 

 coarse and sharp they are termed card-like or cardiform. Teeth set on 

 the jaws and larger than the teeth surrounding them are called canines. 

 On the other hand, some fishes, as the sturgeons and the gizzard shad, 

 are wholly without teeth of any kind. Other interesting organs con- 

 nected with the head are the barbels or beards. Tbey are usually situated 

 near the mouth. Those of the cat-fishes are well, known. In a few min- 

 nows (Hybop)sis semotilus) a small barbel occurs near the corner of the 

 mouth. The body of most fishes is clothed with some sort of firm struc- 

 tures. These are commonly thin, overlapping scales, but, may be hard, 

 bony scales or bony pla'tes. The gars are furnished with a, sort of coat- 

 of mail, composed of imbricated, hard, enameled scales. The sturgeons 

 have five rows of large, bony bucklers. The paddle-fish, the cat tishes 

 and some others are entirely naked. The free borders of the scales of 

 many fishes, as of those of the suckers, pikes and white-fishes, are 

 smooth. Such scales are cycloid. Most of the higher fishes, as the bass 

 and the greater number of the sun-fishes, have the free edge, and often 

 a portion of the exposed surface of the scales provided with numerous 

 sharp points. They are denominated ctenoid scales. In most cases the 

 presence of ctenoid scales may be detected by drawing the tip of the 

 finger lightly over the scales from the tail toward the head. A good lens 



