cciv INFERIOR OOLITE AMMONITES. 



gate, sublatumbilicate. At the same time specimens of X 2 smaller than the actula 

 specimen described should show, but in a reduced form, characters approximating 

 to X 1 (morphic representation), and specimens larger than the type should show, 

 but at a later date, characters which would be expected to belong to X 3 — in a 

 catagenetic series — (morphic prefiguration) . 



There has been no space in the descriptions in this supplement to deal with the 

 ontogeny of each genotype ; but these rules will show what may be expected, and 

 by placing series of allied genera side by side — in which one supplements stages 

 lacking in another — the ontogeny and the phylogeny of the genotypes may be 

 observed. 



When, as types of genetic series, species in different stages of development have 

 been taken, the definition may not only show the difference between them — it may 

 express more or it may indicate less. X smooth is angustumbilicate, Y costate is 

 the same. If smooth X and costate Y be taken as the genotypes, the characters of 

 umbilication appear in the definition as the same, so that apparently the umbilica- 

 tion is not a character of distinction in this case. And yet it may be : the association 

 in which the same umbilicus is found gives the distinction — in X angustumbilication 

 is associated with the smooth stage, but in Y with the costate ; the difference then 

 is between X angustumbilicate -f- smooth, Y the same -\- costate, or, comparing 

 morphic equivalents, which should always be done, between smooth X angust- 

 umbilicate and smooth Y perangustumbilicate. 



These remarks, it is hoped, will make clear the methods which have guided 

 the arrangement of this supplement, wherein an immense series of species had to 

 be dealt with in a limited space. In conclusion, one great difference in the point 

 of view concerning a genus may be brought to mind. Formerly the genus 

 embraced a series of so many homceomorphous species, now the genus comprises 

 what may be called the heteromorphous stages of a phylogenetic series. The 

 difference is most important. In simpler language, once the genus had a horizontal 

 range, now it has a vertical extension. Now the genus indicates a phylogenetic 

 series ; and what is the course of that series is determined by the ontogeny of any 

 one species in it. 



VII. GEOLOGICAL DETAILS. 



The title under which this monograph has been issued is " Inferior Oolite 

 Ammonites," and yet in many cases the species are stated to come from the 

 " Upper Lias." This is not a contradiction ; it only means that the investigations 

 carried on during the progress of this work for the elucidation of the Ammonite 

 horizons have shown the contemporaneity of certain so-called "Inferior Oolite" and 

 certain so-called " Upper Lias " strata. 



The title " Inferior Oolite " was taken in the first place to denote the Inferior 





