246 NATURAL SCIENCE. April, 



succeed one another in the rocks in the same order though in regions 

 far apart. This fact, though extremely important, is in itself not 

 particularly remarkable, since there are other groups of animals 

 whose species have a similarly wide extension in space and a narrow 

 limit in time. The truly remarkable thing is that the same species 

 often occurs in rocks of a very different character, being found in 

 limestones, clays, or sandstones. This may be expressed by saying 

 that the lithological sequence bears no relation to the faunal sequence; 

 and the apparent conclusion is that the evolution of Ammonites was 

 in no way affected by the environment. Taking their stand on some 

 such facts as these, some have even gone so far as to suppose that 

 the rise and fall of any genetic series was an independent pheno- 

 menon, comparable to the life of an individual. This may be, but is 

 it so certain that the facts of Ammonite distribution have any bearing 

 on the question ? 



This question has recently been discussed by Dr. Johannes 

 Walther in the second volume of his " Einleitung in die Geologie als 

 historische Wissenschaft," a volume which deals with the mode of 

 life of marine animals, especially such as are of geological importance. 

 Without offering any opinion as to the zoological affinities of the 

 Ammonites, Dr. Walther points out that their shells, which are 

 practically the only portion with which the geologist has to deal, are 

 paralleled by the shells of only two genera among recent Cephalo- 

 pods, namely. Nautilus and Spinila, which, though differing in every 

 feature of morphological import, yet resemble one another as well as 

 the Ammonites in the possession of a coiled, chambered shell. Now 

 the living Nautilus and Spinila both live at the bottom of the sea and 

 are very restricted in their distribution ; yet their dead shells are 

 found over an enormous area. " In the mangrove swamps of Java, 

 on the sandy shores of Ramesveram, among the volcanic ashes of the 

 Canaries, and on the coral-reefs of the tropical zone ; everywhere are 

 the shells of Spinila found scattered. No coastal deposit in the 

 whole of the Indo-Pacific province is free from Nautilus.''' In these 

 respects Nautilus and Spinila differ from all other living Cephalopods, 

 even from the female Argonauta, whose shell, though outwardly 

 similar, is devoid of chambers ; and just in these respects do they 

 resemble the extinct Ammonites. 



Dr. Walther comes, therefore, to the following conclusions : The 

 distribution of Cephalopod shells provided with air chambers bears 

 no relation to the habits of the living animal. The richness of a 

 deposit in chambered Cephalopod shells does not depend on the 

 distribution or habits of the hving animal. The form of a chambered 

 Cephalopod-shell allows us to frame no safe conclusion as to the 

 organisation of the animal. The distribution of chambered Cephalo- 

 pod-shells bears no relation to the changing character of the 

 containing rock or to the depth of the sea in which it was deposited. 

 Applying these conclusions to the particular case of the Ammonites, 



