CH. XX] SELACHOIDEI 467 



FIG. 227. Scyllium canicula <? . View of viscera from the right side. 



1. Mouth. 2. Spiracle. 3. Gill-slits. 4. Gall-bladder. 5. Oesophagus. 

 6. Pectoral fin cut off. 7. Vesicula seminalis lying on nietanephros. 

 8. Testis. 9. Anterior dorsal fin. 10. Posterior dorsal fin. 



11. Median ventral fin. 12. Dorsal lobe of caudal fin. 13. Ventral 

 lobe of caudal fin. 14. Eight lobe of liver. 15. Proximal limb of 



stomach. 16. Distal limb of stomach. 17. Intestine. 18. Kectum. 

 19. Spleen. 20. Pancreas. 21. Rectal gfand. 22. Bile-duct. 

 23. Claspers. 24. Ligament carrying the vasa efferentia. 25. Vas 

 deferens. a. Coeliac artery. b. Hepatic artery. c. Anterior gastric 

 artery. d. Pancreatic branch of the coeliac artery. e. Anterior 



mesenteric artery. /. Lienogastric artery. g. Posterior mesenteric 

 artery. h. Splenic artery and vein. .;'. Posterior mesenteric artery. 

 k. Portal vein. I. Intestinal vein. 



much detested by fishermen, since they are excessively voracious 

 and their flesh is of little value. Since the beginning of the war, 

 however, the public taste has become more liberal and Elasmobranchs 

 are now largely consumed both in England and also in America where 

 they are known to the trade as "gray fish." 



They are divided into two sub-orders, the Selachoidei and the 

 Batoidei. The first consists of powerful swimmers with cylindrical 

 bodies, well-developed tail fins and moderate pectoral fins ; the 

 latter are ground fish with broad backs and bellies and narrow sides, 

 whip-like tails with rudimentary tail fins, and enormous pectoral fins 

 extending forward to the extreme end of the snout. 



The SELACHOIDEI are known as Dog-fishes or Sharks, according 

 to their size. The common English Dog-fish, Scyllium 



Classification. 9 



canicula, is about two feet long (Figs. 226, 227, and 

 228) ; another kind, the Spiny Dog-fish, Squalus acanthias, is 

 distinguished by having a spine, which is merely an enlarged scale, in 

 front of each of the two dorsal fins. Squalus acanthias is very 

 common on the Atlantic coast of North America, where it is known as 

 the Spiny Dog-fish. The American Smooth Dog-fish, Galeus canis, 

 is distinguished from Scyllium by being viviparous. Amongst the 

 Sharks the most remarkable are Zygaena, the Hammerhead, in 

 which the roofs and floors of the orbits are produced outwards, 

 so that the eyes are set as it were on peduncles ; and Carcharodon, 

 the great White Shark, which has lost its spiracles and possesses 

 a tail-fin with crescentic under lobe. Owing to their powerful 

 swimming capacities, Sharks are as a rule not limited in distribu- 

 tion. Carcharodon is the dreaded man-eater of the Adriatic and 

 the warmer seas everywhere. Zygaena occasionally carries terror 

 into the bay of Naples, and species of both genera are found off the 

 American coast. The Notidanidae are a family with many in- 

 teresting traits. They possess one (Hexanchus) or two (Heptanchus) 

 extra gill-clefts, and the upper jaw directly articulates with the skull 

 behind the orbit. Teeth of the same character as those borne by 



