ELASMOBRANCHn 425 



flashlight bulb. The sting ray or stingaree is very common in the 

 Gulf of Mexico. The average width of those usually seen is from 

 eighteen inches to two feet. They have a long, slender, whiplike 

 tail with a strong spine or sting on the dorsal side of its proximal 

 third. Dasyatis sahina and Dasyatis americaiia are two common 

 forms. The butterfly ray, Pteroplatea micrura, is a broad-bodied 

 form with an exceptionally short tail. They, too, are quite common 

 in the water of the Gulf of Mexico. The sting is usually obsolete in 

 this form. It is called butterfly ray because of the manner of flap- 

 ping the lateral expansions about as a butterfly moves its wings in 

 flight. 



Subclass Holocephali. — This group contains an order with three 

 modern genera. Psychichthys affinis (or Chimaera affinis, as often 

 called) is the only species taken from the waters of the coasts of 

 North America, and then only rarely. Chimaera monstrosa is another 

 species which is found in South American waters. 



Economic Relations of the Class 



Many of the smaller sharks, like Squaliis acanthias and Mustelus 

 canis are very destructive to lobsters, crabs, shrimp, squid, and valu- 

 able fish which they use for food. They also damage much fishing 

 gear by tearing through nets. It is estimated that the damage done 

 in this way averages $400,000 in Massachusetts alone. Along the 

 coasts of California and in the Gulf of Mexico both sharks and rays 

 are a nuisance to the seining fisherman. 



The sting rays or "stingarees" which are armed with the barbed 

 stinging spine on the proximal portion of the tail are generally 

 common in most of the warmer fishing waters. "With a sudden 

 swing of the tail one can inflict an ugly and extremely painful 

 wound. Some people become severely ill as the result of such a 

 sting. Bathers particularly dislike "stingaree" infested beaches as 

 well as those infested with the less common torpedo ray. 



The skins of certain sharks and skates, which have the sharply 

 pointed, toothlike scales, are used as a polisher of wood and other 

 materials and is called shagreen. Shark skins are now being manu- 

 factured into leather on a commercial basis. Large quantities of 

 oil are extracted from some of the sharks, as the cub shark for ex- 

 ample. This oil is used in currying leather in the tanning industry. 



