167 



On the Classification of Mammalia. By Charles Girard, 

 of Washington. 



I. The limits of the class of Mammalia were not clearly un- 

 derstood by the earlier naturalists. Some groups, which in 

 former times were referred to other classes (as Cetacea and 

 Bats), have successively been brought into it. None, how- 

 ever, originally placed in this class have ever required re- 

 moval elsewhere. Thus the progressive investigations has 

 always increased the number of the representative^ of this 

 class. 



At the present day, we may safely say that we know all 

 the essential groups of the class of Mammalia, the actual 

 limits of which are acknowledged by every naturalist. 

 Indeed, we must expect many additional species and genera 

 which time and labour will bring to light, either in a fossil 

 state from various depths in the strata which constitute the 

 solid crust of our globe, or else from its actual surface, and 

 belonging to the living fauna contemporary with the human 

 races. Such additions are not expected to change or modify 

 the boundaries of the class, though they may have some im- 

 portance in the subdivisions and methodical arrangement of 

 the minor groups. 



The division of the class into secondary or minor groups, 

 the relationship and subordination of the latter, have at- 

 tracted the attention of all general writers on zoology. Al- 

 most every one has attempted a classification in accordance 

 with the value attributed to one series of characters, rather 

 than to another. 



The most ancient authors seem to have occupied them- 

 selves but little with zoological characters : hence the sub- 

 divisions which they establish among Mammalia are based 

 upon their mode of life, or the elements in which they live. 



Next we see the subdivisons based upon external charac- 

 ters, the most striking being selected, such as the locomotive 

 members. 



All this prior to the eighteenth century. 



