PISCES 189 



In some species of sharks the young are born alive, but 

 in others the eggs are deposited in a tough, usually flattened 

 case with tendrils by which it may be fixed to seaweeds. 

 Most of the one hundred and fifty species of sharks are 

 characterized by five gill openings on either side of the head, 

 underneath which the mouth is situated. 



The rays differ from the sharks in having the gill open- 

 ings beneath the flat disk formed by the body and the ex- 

 panded pectoral fins. The common skate of our Atlantic 

 coast (Raja erinacea) grows to a length of nearly two feet 

 and is nearly as broad. The sawfishes, some of which are 

 fifteen feet long, are remarkable for the prolongation of the 

 snout in a saw-edged sword nearly one fourth the length 

 of the fish. They range from Cape Cod southward. Not 

 less noted is the electrical fish (Torpedo marmoratus) found 

 along the New England coast. A specimen two or three 

 feet long is capable of imparting a severe shock to any one 

 seizing it along the sides of the body. 



Bony Fish (Teleostomi). This order is made up of 



FIG. 219. The bull head (a catfish). Photograph one fourth natural size. 



thousands of species which are characterized by a bony 

 skeleton, usually a scale-covered body, and gills protected 

 by a plate projecting backward called the operculum. 



