CHAPTER XXVI 

 THE ELASMOBRANCH FISHES SCYLLIUM CANICULA 



AMONG the oldest remains of vertebrated animals that have 

 been discovered are teeth and spines, whose structure shows 

 clearly that they belonged to fishes resembling our modern 

 sharks and dog-fishes, and some wonderfully complete speci- 

 mens of ancient sharks have been obtained from carboniferous 

 deposits. The sharks, then, belong to a very ancient group of 

 fishes, and, as might be expected, the living forms retain so 

 much that is primitive in their organisation, that they are 

 beyond all other animals instructive to the comparative 

 anatomist. If. Amphioxus affords us a clue to the general 

 architecture of vertebrated animals, the sharks, dogfishes, and 

 rays are no less important as giving us an insight' into the 

 anatomy of craniate and gnathostomatous vertebrates that is, 

 to vertebrates which have a distinct head, furnished with true 

 jaws. 



The larger forms of sharks are happily not common in 

 British waters, though some of them occasionally wander to 

 our coasts. But dogfishes, which, to all intents and purposes, 

 are little sharks, are very abundant and of several kinds. 



One of the commonest is Scyllium canicula, known to fisher- 

 men as the "little rough dog." It is also called the " rough 

 hound," the "lesser spotted dogfish," and other names. A 

 somewhat larger and closely allied species is the " nurse 

 hound" or "greater spotted dogfish," Scyllium catulus, but it 

 is not so common as Scyllium canicula. Besides these, are the 

 "Toper," Galeuscanis\ the "smooth hound," Mustelus lcevis\ 

 and the "picked dog," Acanthias vulgaris. The last named is 

 .extremely common,, and is easily recognised by its bluish-grey 

 back, its white belly, and by the sharp-pointed, powerful spine 

 situated in front of each of the two dorsal fins. The skates 

 and rays, though differing greatly in appearance, are closely 

 allied to the sharks and dogfishes, their wide flattened shape 

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