THE LOWER FISHES 



165 



Coast form. It reaches 4 feet or over and ranges from central California to the 

 Gulf of California. 



The mottled guitarfish, Zapteryx exasperata, has a shortened snout, wider 

 disc, dark crossbands, and reaches 3 feet in length. It is found from San Diego 

 to Panama. 



The thornback, Platyrhinoidis triseriata, has a skatelike rounded disc and skate- 

 like spines on the back and shoulders. It reaches 3 feet and is found from 

 central California to Baja California. 



Skates: Superfamily Rajoidea 



In these rays and all remaining rays, the tail is sharply marked off from the 

 body, and the pectorals are the chief means of locomotion. Skates also have 

 the dorsal and tail fins greatly reduced in size and the pelvic fins deeply notched 

 so that they look double. The males possess very large claspers. The discs and 

 tail are covered with enlarged prickles in patches which vary according to species. 

 Skates are characteristic of temperate and arctic waters of the world. They are 

 in the tropics, but only in very deep water. Some run up rivers. They are the 

 onlv oviparous rays. The egg cases, called "sea purses' or "sailor's purses," are 

 very common objects on beaches. 



SKATES: Family Rajidae 



This is the only family of skates and contains the largest of all elasmobranch 

 genera, Raja, with almost a hundred species. The species of this genus have 



E&G CASE X-r 



Figs. 7?) and 74. Common skate Qeft^ and spotted guitarfish (rig^it). 



