﻿238 BRITISH FOSSIL CEPHALOPODA. . 



Coming next to the groups, we see that the last-made observation is more 

 especially applicable to the Conici, and that it was the more or less abnormal groups 

 of the Inflati and Irregulares which could best abide the clearer waters of a coral 

 reef. Of the four groups the Conici first appear, and form the bulk of the Lower 

 Silurian fauna, the other groups making but little real show before the Upper 

 Silurian period. The Conici and Spirales are the only two groups which continue 

 to flourish in later periods. The Inflati have only a few representatives in the 

 carboniferous Poteriocerata ; the Irregulares, if occurring at all, being represented 

 by different genera. These two groups must therefore be looked upon as offshoots 

 from the main stem, which attained their maxima in the Lower Ludlow period, when 

 the whole class were most flourishing, and then rapidly died away. We obtain from 

 these facts independent confirmation of laws which appear to widely govern the 

 development of life, and which may be thus stated : — 



The simpler forms in a class are the first to be introduced, and the more 

 complex appear later. It is only when the class is in its most flourishing condition, 

 and not long before the close of a period, that it throws out the more remark- 

 able and abnormal forms. The group which represents somewhat the mean of 

 the whole and never attains an extraordinary abundance, as the Spirales, is the 

 longest to last. 



We must next consider the individual genera. The first to appear is Cyrtoceras, 

 represented by the species C. pruecox, though followed in the uppermost division of 

 the same rocks by Orthoceras sericeum. It has been thought remarkable that the 

 less simple form should precede the straight Orthoceras, but the history of discovery 

 shows that we can place but little trust in such an isolated fact, which is liable any 

 day to be reversed. Nevertheless, on any theory of evolution, the present state of 

 the case is just what we might expect ; for the lower groups from which the 

 Cephalopoda might be derived are not straight, like an Orthoceras, but curved, like 

 a Cyrtoceras : in fact, the absence of curvature is obviously only a particular case, 

 while some amount represents the general idea. Moreover, if we are to look to 

 individual development as the summing up of the history or ontogeny of the 

 group, we should expect from the frequent curvature exhibited near the apex in 

 the Orthocerata that their ancestors were curved. 



Neither the first Orthoceras nor the first Cyrtoceras are transitional forms ; both 

 are well characterised. It is true that in neither is the siphuncle actually seen, 

 but it is indicated ; and it is only the state of preservation of the fossils that 

 prevents us from seeing it better. Unless, therefore, we are prepared to believe 

 that life in its various forms sprang into existence at the period in whose deposits 

 we first find their remains, we must admit that there were Cephalopods during 

 the oldest Cambrian or even the pre-Cambrian periods ; and hence the fact of 

 earlier forms being found in Sweden and England than occur in Bohemia loses 



