FISHES AND FISHERIES 247 



fishing grounds not only on account of the fact that they kill 

 but because they drive away the schools of fish and squid and 

 destroy the nets and traps. 



The skates and rays have a broad, flattened body with the 

 gill-openings on the underside. They are usually sluggish, 

 lying at the bottom of shallow waters along the shore feeding 

 on crabs, molluscs and bottom fishes. The small common 

 skates, or "tobacco-boxes," Raja erinacea, which reach a 

 length of about twenty inches, and the larger "barn-door 

 skates," R. lizvis, are numerous along the Atlantic Coast. 

 The sting-rays, genus Dasyatis, which lie in the sand in shallow 

 water, have a barbed spine on their whip-like tail which makes 

 a very painful wound. The torpedoes, or electric-rays, have, 

 on either side of the head, modified bundles of muscles which 

 store up considerable electric energy. The discharge from 

 these electric organs can give a strong shock to animals coming 

 in contact with them. It is said that a discharge from a 

 large electric-ray is sufficient to disable a man temporarily. 

 The saw-fish, Pristis pectinatus, differs from the typical rays 

 by having the body more elongate and shark-like. The head 

 is prolonged into a long saw-like snout which may reach a 

 length of five feet or more. This may be used as a weapon of 

 defense or to kill the small sardines and herring upon which 

 the saw-fishes feed. 



The Chimaeras, or "Elephant Fishes" (sub-class Holo- 

 cephali). These fishes compose a small group of peculiar 

 forms looking somewhat like the smaller sharks. Most of them 

 live in deep water, but others are rather common in the 

 shallow water of bays along both coasts of America and else- 

 where. They are of very little economic importance. 



The True Fishes (sub-class Teleostomi). -To this sub-class 

 belong nearly all of our common fishes, both of fresh water 

 and ocean. In most of them the skeleton is bony and not 

 cartilaginous as in the sharks and rays. The sturgeons, 

 family Acipenseridce, are the notable exception to this rule, as 

 their skeleton is cartilaginous. In the garpikes and a few 

 others the skeleton is only partly bony. The sturgeons occur 

 in both salt and fresh water, some of them attaining a weight 



