6 NORTH AMERICAN INDEX FOSSILS. 



the same for all genders and commonly terminate in i. The Greek 

 ending oides remains the same in all genders. A generic name be- 

 comes a synonym when it is found that the same name has pre- 

 viously been used for an organism of another genus. It must then 

 be replaced by another name. A specific name becomes a syno- 

 nym when the genus in which it belongs already has a species 

 of that name. Different genera may have species of the same name. 

 Sometimes an author describes and figures under the same name 

 several forms which are subsequently found to belong to distinct 

 species or even genera. In all such cases new names must be 

 used, the old names becoming synonyms for that species or genus, 

 though holding good for the forms to which they were originally 

 applied. In some cases a species or genus already named or a 

 form belonging to a species or genus already established is given 

 a new name by a later author. This new name then becomes a 

 synonym and unless restored to rank subsequently for the typefot 

 which it was proposed, has no value whatever, but is dead. It can 

 never be used again. 



Table of the Animal Kingdom. 



The following table of the animal kingdom takes account only 

 of those classes which are represented among fossils, or, in other 

 words, only such which have hard parts capable of preservation. 

 The classes and subclasses in italics will be omitted in the succeed- 

 ing discussions : 



Phylum. 



IX. Veitebrata 



Branch. 



VIII. Echinodermata.. \ 2 \ 



Class. 



Mammalia. 

 Aves (Birds). 

 Reptilia. 

 Amphibia. 

 Pisces (Fishes). 



* \ 



Subclass. 



f 



Holothuroidea (Holo- 



thurians. ) 

 Echinoidea ( Sea Urchins ) . 



Asteroidea (Starfish). 

 Ophiuroidea (Brittle 

 stars). 



I 



Crinoidea. 

 Blastoidea. 

 Cystoidea. 



