THE LOWER FISHES 167 



prominent row of spines on the midline of the back and tail. The whole 

 tail is covered with thorns of like size. The back is spotted or barred with 

 dark brown. Reaches 2 feet in length. Found in shallow waters from 

 Maine to Florida but common only from Massachusetts to Delaware. 



3. Barndoor Skate (Sharp-Nosed Skate): Raja laevis 



The popular name is derived from its large size, which may attain a 

 length of 5 feet and a weight of 35 pounds. The snout is prolonged and 

 pointed and the body spines small. It is the only skate with pigmented 

 mucus pores on the underside. Found from Newfoundland to Cape 

 Hatteras. 

 West Coast: 



4. California Skate: Raja inornata 



The outer border of the pelvic fin is deeply concave and the color is 

 dark olive to brown with vague mottlings. It reaches 2^2 feet. Found from 

 the Strait of Juan de Fuca in the North Pacific south to Cedros Island, 

 California. 



5. Big Skate: Raja hinoculata 



There is a large ocellar spot on the inner side of each pectoral fin. The 

 outer border of the pelvic is nearly straight. It reaches 6 to 8 feet in length 

 and the egg cases are a foot long and contain up to seven eggs. Found from 

 Alaska to southern California. 



6. Long- Nosed Skate: Raja rhina 



The snout on this skate is very long and tapering. The overall size may 

 reach 4 to 5 feet. Found from Alaska to southern California. 



Electric Rays: Superfamily Torpedinoidea 



These are very odd rays possessing an almost circular disc and a stout, some- 

 what sharklike tail on which are situated two large dorsal fins and a large tail 

 fin. The eyes are small; some electric rays are even blind. The body is smooth 

 and peculiarly flabby. The pectoral fins are thick and rather immobile, being 

 the seat of the large electric organs, which may weigh as much as one-sixth 

 of the total weight. Because of the fact that typical muscle nerves go to these 

 organs, they are thought to be a muscle tissue in which the electrical properties 

 inherent in all muscle tissue have been accentuated at the expense of the 

 locomotory properties. They are formed of thousands of hexagonal discs piled 

 in columns and thus look like honeycombs. The resemblance to a voltaic pile is 

 striking. A shock delivered by these rays is really a "train" of twelve to a hundred 

 separate pulses each of which lasts about three hundredths of a second. Voltages 

 delivered vary from eight to 220 depending upon the size of the ray and its 

 species. Several shocks may be delivered in succession, but each one is a little 

 weaker than its predecessor. A rest period is needed to build up the power to 

 its full state again. The shocking power is far less than the really dangerous 

 electric "eel," Electrofhorus, of South American rivers. Still, it is enough to 

 knock down and temporarily disable a full-grown man. 



The purpose of the shocking power is a matter of some mystery. Almost 

 certainly, it is defensive, and it seems likely that it may also be offensive. 

 Presumably, electric rays are too slow-moving to catch the fishes, such as dogfish 



