342 GEOGRAPHICAL AND GEOLOGICAL DISTRIBUTION. 



tification. The members of this genus are probably the largest of 

 all living animals, some of the forms, as Balsenoptera Sibbaldii 

 and B. sulfurea, attaining a length of eighty or perhaps even a hun- 

 dred feet. The smallest of the known species of whalebone whales 

 is the rare Neobalasna marginata, from the Australian and New 

 Zealand seas, which attains a greatest length of about twenty feet. 



Of the toothed-whales, other than the members of the family 

 Delphinidaa (dolphins, porpoises, &c.), the best known and prob- 

 ably most widely distributed species is the cachalot or sperm-whale 

 (Physeter macrocephalus), a giant form measuring upwards of sixty 

 feet in length, whose habitat is more properly the tropical and sub- 

 tropical seas, the animal but rarely appearing in the polar waters. 

 More or less closely related forms of the same family (Physeteridee) 

 are Kogia, Ziphius, and Mesoplodon, the species in each group of 

 which have either individually or collectively a very broad exten- 

 sion.* Two species of bottle-nose whale (Hyperoodon rostratus 

 and H. latifrons) inhabit the North Atlantic. 



Of the delphinoid type of cetaceans the most numerously repre- 

 sented genus is Delphinus, the dolphin, or, as it is frequently mis- 

 called, porpoise, the numerous species of which are distributed 

 throughout most seas, a limited number even habitually ascending 

 some of the larger streams, as the Amazon. The type-form of the 

 genus is the common or Mediterranean dolphin, the hiqros iclitliys 

 or sacred fish of the ancients (D. delphis), which is also abundant 

 in the Atlantic, and of which closely allied, if not identical, forms 

 are found in the Australian seas (D. Forsteri) and in the North 

 Pacific (D. Bairdii). 124 One of the most northerly species of dolphin 

 is the tursio, or nesarnak of the Greenlanders (D. tuisio), which 

 inhabits the Atlantic between Greenland and the European shores. 

 Modifications of the ordinary delphinoid type are seen in the long- 

 beaked forms of the group Steno, and in a South Sea species, Leu- 

 corhamphus (Delphinapterus) Peronii, in which there is no dorsal 

 fin. The bottle-heads (Globicephalus) are inhabitants of nearly all 



* Much diversity of opinion exists as to the number of species belonging to 

 the different genera. Thus, -while Gray recognised not less than six species 

 of Kogia, founded upon about as many individual specimens, only one (Kogia 

 breviceps, found in the South and North Pacific oceans) is admitted by 

 Flower (" Encycl. Brit.," 9th ed., xv., p. 396). The same authority likewise 

 considers the species of the other genera as being in great part founded upon 

 insufficient characters. 



