184 . V. PRINCIPLES OF 



The CLASS (Classis) is the highest or first divi- 

 sion in each of the three kingdoms of natural bodies 

 (. 1) Reliquia may be considered as forming one 

 class in the mineral or fossil kingdom. 



The ORDER (Ordo*) is a division of the class f. 

 In the arrangement of extraneous fossils, the orders 

 may be founded on the two kingdoms of organic 

 bodies from which they receive their form namely 

 animals and plants. 



The GENUS (Genus] is a division of the order. 

 Genera are either natural or artificial f f. 



The natural genera of reliquia are those which 

 are founded on the natural classes, orders, or other 

 primary divisions of plants and animals, e. g. 



under a genus, or the genera under an order it has been 

 found convenient to separate such species or genera by secondary 

 or .swfr-divisions. In our arrangement of extraneous fossils, we 

 have denominated the subdivisions, under the genus, families. 



f Orders are usually arbitrary divisions. In Botany, they arc 

 confessedly artificial, at least in the Linnean system adopted to 

 assist the investigation of the genera, by bringing together those 

 that agree in the number and form of certain parts ; which agreement 

 is considered as characteristic of such divisions or orders In a 

 system of extraneous fossils, where the genera are necessarily few, 

 the order is scarcely wanted for a division ; but we have used it 

 in conformity with the Linnean principles of arrangement. 



-ft A natural genus, or other division, in Botany and Zoology, is 

 usually considered to be one which comprehends only such species 

 as are naturally allied to each other ; and, consequently, agreeing 

 in a great number of external characteristics an artificial genus, or 

 order, one in which the species arranged under it, evidently differ 

 in most particulars, except those few which have been fixed on as 

 diagnostics of the division, 



