WHALES. 341 



seven species of fossil Sirenia, as widely distributed then as the 

 recent forms are at the present day, but with a range from the 

 Tropic of Cancer up to CO of north latitude, affords a most valua- 

 ble piece of evidence (if such were needed) attesting the former 

 northern extension of subtropical conditions of climate which must 

 have prevailed over Europe, Asia, and North America, in Eocene 

 and Miocene times, and in the older Pliocene also." 123 



Cetacea (Whales, &c.). The animals of this order are distrib- 

 uted throughout almost the entire oceanic expanse, and a limited 

 number of forms, the members of the family Platanistidae, and 

 some delphinoids, are also found in fresh or estuarine waters. 

 Platanista Gangetica, an inhabitant of the waters of Northern India 

 Ganges, Brahmaputra, and Indus, and their tributaries is en- 

 tirely fluviatile, never being known to pass out to sea The only 

 absolutely fluviatile form occurring in America is Inia Geoffrensis, 

 from the Upper Amazonian water system ; Pontoporia Blainvillii 

 inhabits the estuary of the Rio de la Plata, but is not positively 

 known to ascend that stream into fresh water. 



Of the marine cetaceans two distinct types are usually recog- 

 nised by naturalists : the whalebone or toothless whales (Mystaco- 

 ceti), as represented by the right-whales (Balacna), rorquals, or fin- 

 whales (Balaenoptera), and the humpbacks (Megaptera). and the 

 toothed-whales (Odontoceti), which comprise the sperm-whales, 

 dolphin, porpoise, grampus, &c. The right-whales, which are 

 confined principally to the northern and southern seas, have been 

 divided into some half-dozen species, which, however, so closely 

 resemble one another that not improbably they represent only vari- 

 etal forms of one and the same species. The best known is the 

 Greenland right-whale (Balsena mysticetus) of the Arctic seas ; 

 other .northern forms are B. Biscayensis and B. Japonica. The 

 southern species or varieties are B. australis, of the South Atlantic, 

 and B. antipodarum and B. Novse-Zelandiaa, of the South Pacific. 

 A nearly equal uncertainty attaches to the different varieties or 

 species of rorquals and humpbacks, especially the latter, some 

 forms of which are found in almost every sea. Four or more ap- 

 parently distinct types of rorqual inhabit the northern seas, but 

 whether these are absolutely separable from their antipodal con- 

 geners still remains to be determined. Much confusion exists as to 

 the synonymy of the species ; hence, the great difficulty of their iden- 



