SONNINIA— SUMMARY. 451 



they exhibit. From spinifera, however, they are more than specifically distin- 

 guished ; for spinifera lacks altogether that very strength of ornamentation which 

 these species possess in common. 



The series arranged under II, C, C (p. 390), may be regarded as generically 

 distinct because of the asymmetry of L, which, however, remains very long. (Of 

 course these features do not separate acanthodes and reclinans, because in them such 

 characters have not begun to be apparent : they, however, bear indications in their 

 ornament as to which groups they belong to.) Then the series II, C, C, is further 

 separable according to the stage of phyletic retrogression at which the abbreviation 

 of the inner lateral lobule of L makes the asymmetry pronounced — in series II, 

 C, G, a, it is apparent in the spinous stage ; in series II, C, G, j3, it is but slight in the 

 costate stage. All the species grouped under II, D are very well separated by the 

 extreme development of their septation and the tendency to " renovation " — to 

 acquire larger costas, or even tubercles, after a period of decline. It will be 

 interesting for anyone to note how greatly they differ in respect of the septation 

 from such a form as dominatrix, to which PI. XCIV bears witness ; and also they 

 differ remarkably from all the short-lobed species classed in II, A. In these cases 

 a generic distinction could be perceived without any difficulty. It is points like 

 these that the classification and the genealogy have been constructed to illustrate. 

 The attempt has been made, as far as possible, to place closest together those 

 species which have the greatest number of characters in common, and to place 

 furthest apart those which have the fewest. This, in fact, is the aim of all classi- 

 fications — and a true classification should be synonymous with the genealogy. A 

 failure to be so arises from the fact that certain striking characters have made too 

 great an impression on the observer, while he has overlooked some more or less 

 obscure characters which are really more faithful guides. In a natural classifica- 

 tion obscure characters may be far more important than those which so readily 

 attract the eve. 



Nothing, perhaps, is more remarkable than the fact that in all the literature 

 on Ammonites not one of the Sonninise of the Concavum-zone has been 

 figured before. Such a series of species altogether new to science is rather 

 remarkable, but not one of them can be compared with any figure previously 

 given. The only species at all like them are illustrated in Quenstedt's " Amm. 

 Schwabischen Jura," pis. lx — lxiii, but many of those species are perfectly well 

 known in Dorset as occupants of a distinctly higher horizon. 1 Those and their 

 allies it will be my task to figure in Vol. II. 



That European literature contains no figures of any of the Concavum-zone 

 Sonninids certainly shows how little the Concavum-bed is developed on the 



1 "The Bajocian of the Sherborne District," ' Quart. Journ. Geol. Soc.,' vol. xlix, p. 494. 



