248 PRINCIPLES OF ANIMAL BIOLOGY 



each of these ranks. So regular is this practice that if there were only 

 one kind of animal in a phylum, it would probably be assigned also to a 

 named class, an order, and a family, as well as a genus and a species. 

 The other ranks named are used for some groups or by some naturalists. 

 The rank of recognized categories may be expressed as follows: 



Phylum. Example, Chordata (the chordates) 



Subphylum. Example, Vertebrata (the vertebrates) 

 Class. Example, Mammalia (the mammals) 



Subclass. P]xample, Eutheria (the placental mammals) 

 Order. E>xample, Rode7itia (the rodents) 



Suborder. Example, Sciuromorpha (the squirrellike rodents) 



Family. Example, Sciuridae (the flying squirrels, marmots, squirrels, 

 chipmimks) 

 Subfamily. Example, Sciurinae (marmots, squirrels, chipmunks) 

 Genus. Example, Sciurus (the arboreal squirrels) 



Subgenus. Example, Tamiasciurus (the red squirrels) 



Species. P^xample, hudsonicus (the Hudsonian red squirrel) 

 Subspecies. Example, loqiiax (the southern Hudsonian 

 red squirrel) 



In some grovips "divisions" or '^sections" are recognized by authors, 

 but these categories have no definite place in the system; that is, they 

 may be introduced to mark off a group of genera, an assemblage of orders, 

 etc. 



The Linnaean system designates the species by two Latin or latinized 

 names, the generic name, a noun, and the specific name, usually an adjec- 

 tive. Thus Natrix is the generic name of a group of water snakes, and 

 Matrix rhomhifera and Natrix sipedon are two species of water snakes. 

 This is known as the binomial system of nomenclature. When subspecies 

 are recognized, three names are used — the generic, the specific, and the 

 subspecific — thus: Thamnophis sirtalis parictalis. Subspecies must 

 usually have somewhat separate geographic ranges, but they grade into 

 the neighboring subspecies at their common l:)oundaries. The term 

 variety, sometimes carelessly used synonymously with subspecies, often 

 means only a genetically different type of individual not having geo- 

 graphic separation, for which the word phase is a preferable designation. 

 Thus, the cinnamon individuals that occur not infrequently throughout 

 the range of the black bear, Euarctos americanus, to which species it 

 Ix'longs, may be called a phase or variety. Such varieties are not ordi- 

 narily named in the Linnaean scheme. However, the taxonomic rank 

 of variety may be assignc^l to divisions smaliei- than subspecies, and in 

 one group, the ants (family Formicidae), the systematists regularly 

 recognize and designate divisions smaller than sul).spe('ies by name, using 

 four names for each variety (for example, Camponotus hcrculeanus 

 ligniperdus noveboracensis, the northern carpenter ant). 



