CLASSIFICATION 663 



porpoises, and dolphins. They have teeth but no whale-bone. They 

 possess a single nostril or "blow-hole" and some of the ribs are two- 

 headed. 



Order XIII. Mystacoceti (Whale-bone whales). 



These are also called baleen whales. 



For convenience sake the following terms are often used : 

 Ichthyopsida. 



This is a name given to Cyclostomes, Gnathostomes, and Amphibia 

 combined. The distinctive characteristics of the Ichthyopsida are that 

 all animals belonging to this group breathe by means of gills at some 

 period of their life's history. They are therefore, aquatic vertebrates. 



They are sometimes called Anamniota or Anamnia because they do 

 not develop an amnion, and Anallantoida because they do not develop an 

 allantois. 

 Sauropsida. 



This is the name given to birds and reptiles combined. The dis- 

 tinctive characteristics of the Sauropsida are, that all animals belonging 

 to this group breath with lungs and never develop functional gills : They 

 are therefore terrestrial vertebrates. Sauropsida, together with the 

 Mammalia, are called Amniota on account of their developing an am- 

 nion, and Allantoida on account of their developing an allantois. 

 Tetrapoda. 



This is the collective name assigned to all four limbed animals, 

 whether they are amphibians, reptiles, or mammals. 



