290 Zoological Principles of Classification^ 



more profound examination would liave shewed that they in- 

 dicate nothing on the most essential points of the organism.* 



The classification of fossils, therefore, must necessarily be 

 based on considerations of this nature, and on the constant 

 study of living nature. If we neglect this the only certain 

 method, we cannot confer on this science the advantages of 

 the natural method. And it is not only for establishing the 

 great divisions that these precautions are necessary ; the ob- 

 servations made above are in every respect applicable to the 

 formation of genera and the grouping of species. We shall 

 even frequently find, that if palaeontologists confine them- 

 selves to these necessary rules, the study of fossil bodies will 

 react on the natural methods, and thus improve the classifi- 

 cation of living animals. 



Nearly the same things may be said of the determination 

 of fossils, as have been stated respecting their classification. 

 The same general principles which direct the zoologist in re- 

 cognising living species, ought to apply to the determination 

 of fossil animals ; but as, in many cases, we possess only 

 fragments, it is necessary that a more rigorous analysis 

 should be applied to this determination by more restricted 

 methods. 



It is particularly with the vertebrate animals that it is ne- 

 cessary for the palaeontologist to proceed on laws and fixed 

 methods, because we are seldom acquainted with these ani- 

 mals but by means of a small number of bones, which may 

 furnish vague and erroneous conclusions to superficial ob- 



* Thus, in regard to bivalve shells, the study of the living molluscs 

 will shew that the fact of being equivalve or inequivalve is of great im- 

 portance, because the station of the molluscs depends upon it ; for such 

 of these animals as have two equal valves keep themselves erect, while 

 those with a large and small valve lie on their side. This study will 

 also prove that the form of the impression of the mantle is intimately 

 connected with the presence and size of the tubes ; and that, conse- 

 quently, the fact that this impression is, or is not, notched by a sinus, 

 may furnish a character of great importance. This same observation 

 of living nature will lead us, on the contrary, to ascribe little import- 

 ance to the existence of one or two muscular impressions, inasmuch 

 as it is of little consequence whether the shell be closed by one or two 

 muscles. 



