246 THE MAMMALS OF THE NORTH ATLANTIC 



the back. In many cases the fin has horny tubercles on the fore-edge, and it is always 



longer along the base than it is high. The species is widely distributed, not only 



in the North Atlantic but also in the North Pacific, where it ranges from Alaska 



to Mexico. It generally keeps near the coast, but will swim up large rivers for 



a considerable distance in quest of food. Porpoises feed exclusively on fish. The 



members of a shoal, alternately rising and diving as they swim, form one of the most 



interesting sights of the sea. 



The beaked whales (Ziphiidce) and sperm-whales (Physeteridce) 

 Beaked Whales. , 



form family groups, distinguished, among other features, from the 



majority of dolphins by the absence of teeth in the upper jaw, at least in the existing 



members of the group. The beaked whales have, at most, a single pair of teeth in 



the lower jaw, which are placed about the middle of its length, and are more or less 



laterally compressed, so much so, indeed, in some cases as to assume a strap-like 



form. The commonest species is Sowerby's beaked whale (Mesoplodon bidens), 



attaining a length of about 15 feet, and characterised by the rather small teeth 



which in some cases project but little above the edges of the mouth when closed. 



The long beak is nearly straight, and above it the head gradually curves upwards 



so as to form a fairly high protuberance in front of the blow-hole, while behind 



there is a second step which gradually merges into the line of the back 



cuvier's Beaked Cuvier's beaked whale (Ziphius cavirostris), although but seldom 



whale. me t with, appears to be of world-wide distribution. It is distin- 

 guished by the two conical teeth at the tip of the lower jaw, as well as by the 

 circumstance that only the first three vertebrae of the neck are fused together. In 

 the bottle-nosed whale all seven of these vertebrae are united. 

 Bottle-Nosed The bottle-nosed whale {Hyp>eroodon rostratus), is a near ally, 



wnaie. generally seen in schools, or " gams " as they are called, whereas the 

 beaked whales are generally met with alone or in pairs. These whales have the 

 back-fin sickle- shaped and situated a little behind the centre of the back ; the head 

 rises abruptly from the beak, protected by a cushion of fat in front of the crescent- 

 shaped blow-hole. They differ from the cachalot and resemble the beaked whales 

 in having only one or two pairs of teeth in the lower jaw, which are largest in the 

 males. This sex attains a length of 30 feet, but the females do not exceed 24 feet. 

 The bottle-nose ranges south to the English Channel, and as far north as the Arctic 

 Circle, or even a few degrees beyond, and although more frequently stranded on 

 the British coasts than any other whale, is more of a deep-water species than any 

 of those mentioned above. 



With the fin-whales, or rorquals, we reach the first representatives 

 of the second great group of cetaceans, the whalebone whales, or 

 Mystacoceti. These are distinguished by the development of plates of whalebone 

 from the whole surface of the upper jaw, by means of which they strain off 

 the water taken into the mouth with their food, which may consist of fish of con- 

 siderable size or of minute organisms floating on the surface of the sea. The members 

 of this group take their name of fin-whales from the presence of a small back-fin, 

 and their Norse designation of rorquals from the flutings on the collapsible pouch 

 on the throat when in its contracted condition. On account of the presence of this 

 pouch, in which the food is contained, the whalebone is very short, and of no 



