352 PLAGIOSTOMES. 



The Chimaeras form a connecting link between the 

 preceding and the Sharks. 



KiG. 234. — NURTHEliX CHIM.ERA. 



Cartilaginous Fishes with Fixed Braxchi^e. 

 Choxdropterygii Branchiis Fixis. 



In this division of cartilaginous fishes the gills, 

 instead of beins: free on tlieir external edo-e and sus- 

 pended in a common cavity, from which the water 

 escapes by a single opening, are adherent to tlie 

 skin, so that for the escape of the water that passes 

 over them there are as many openings as there are 

 intervals between the branchiae. In other respects 

 these fishes differ very much from each other. They 

 are divided into two orders, distinguished by the 

 structure of their jaws, viz.. 



The Plag-iostomes* and the Cyclostomes.t 



Order of Plagiostomes. 



This Order comprises the Sharks and the Eays, or 

 Skates. They have both pectoral and ventral fins, 

 five, branchial openings on each side of the neck, or 

 on its inferior face, and the jaws are armed with 

 teeth. Thev lay eggs covered with a hard horny 

 shell (Fig. 286). 



The Sharks (Squalidse) are recognisable by their 



* irkdyios, plagios, oblique ; a-rofxa, stoma, the mouth; — having their 

 mouths placed transversely. 



t KVK\os, cyclos, a circle ; crrofxa, stoma, the mouth ; — having circu- 

 lar mouths. 



