46 NOTICES OF NEW BOOKS. 



laeontologist is bound to consider them as distinct species in the pre- 

 sent state of science. He will in this way bring together facts that 

 may be compared ; and the limits of species will possess for him a 

 clearness which they cannot have if it is admitted that they may 

 vary in a manner not admitting of strict definition, and from the in- 

 fluence of causes which escape detection for the very reason that 

 they are supposed to be different from those which act at present*. 



" The group of subanalogous species seems to me no better esta- 

 blished than the analogous ones ; for if the shells so designated differ 

 by characters too important to allow of their being referred to the 

 same species, it is clear that in the view of the question we are now 

 taking, this word is synonymous with different or extinct species. 



" I think therefore that it is more proper and more conformable to 

 facts, not to take account at present of these intermediate degrees of 

 analogy ; but in discussing the law of the speciality of fossils, to 

 apply to the investigation of these remains of ancient animals the 

 same laws which guide the naturalist in the establishment of exist- 

 ing species. The distinctions established by M. Defrance will still 

 be useful in the comparison of the extinct species of different geo- 

 logical faunas, since it may often be a matter of interest to know 

 the greater or less degree of resemblance that exists between such 

 species and those which preceded or succeeded them. 



" This point being established, the question is simplified, and its 

 solution depends entirely on the examination of facts under the 

 guidance of zoological principles properly so called. It may seem 

 then that we have only to compare the lists of the fossils of each 

 formation as established by palaeontologists, in order to see whether 

 the same names are repeated ; but unfortunately these lists, often 

 prepared hastily, and sometimes by superficial observers, or by those 

 little versed in zoology, are not always such as to inspire confidence, 

 and indeed most of them abound with errors. The result of the 

 comparison, if these lists are taken, is, that many species occur in 

 more than one formation ; but the more carefully fossils are studied, 



* "These strict limitations in laying the foundation of our argument by no means 

 prevent subsequent discussion concerning the prolonged influence of external 

 agents ; and I think that the partisans of the theory of the passage of species 

 from one formation to another must necessarily grant so much as a point of de- 

 parture. Logically there are for them but two courses to take ; namely, either to 

 limit, as we have done, the determination of fossil species by the same principles 

 as those which are introduced with regard to existing nature, or else to reunite as 

 the same species all those animals which they consider to have proceeded from the 

 same type. Now if this last method is followed, a mischievous variability is in- 

 troduced with regard to the limits of specific character. One naturalist will group 

 together only certain animals which seem to him to possess resemblances too con- 

 siderable to admit of other than a common origin. Others, adopting to a greater 

 extent the theory of gradual development, will associate under a common specific 

 name, genera and even whole families which they look upon as forming a series of 

 modifications of a primitive type. There is no longer either fixed rule or unity. 

 I am indeed well-aware that these extreme results are far from according with 

 the views of the learned conchologist whose opinions I am combating, but it is 

 dangerous to advance even a single step in a wrong direction, lest we should be 

 obliged to follow out such a mistaken route to extremity." 



