398 INFERIOR OOLITE AMMONITES. 



Sonninia ueassa, 8. Buckman. Plate 0, fig. 10. 



See Plate LXXXII, figs. 1, 2, and page 350. 



Add to description : — Suture-line with fairly long lobes ; with slightly intra- 

 axial, isosceloid, terminal lobule, lateral lobules slightly anisometric, the outer dis- 

 tinctly bipartite. 



2. Terminal lobule anisosceloid. 



Fig. 35. — Outline of L of Sonn. diversa. 



Sonninia crassicostata, 8. Buckman. Plate GUI, fig. 18. 

 See Plate LXXX, figs. 4—6, and page 354. 



Add to description : — Suture-line of type with lobes fairly long ; L with axial, 

 ectobrachysceles terminal lobule, and practically isometric lateral lobules. 



The suture-line of the type is somewhat abnormal, and hardly seems to 

 warrant the present position of the species. The terminal lobule of L is ecto- 

 brachysceles, whereas in the outline given above (fig. 35) the terminal lobule is 

 anisosceloid by reason of being endo-brachysceles. 



Perhaps the ecto-brachysceles character in the type is due to an exceptional 

 development of an accessory lobule beyond (above) the outer lateral lobule and at 

 its expense; and that normally the suture-line of the species more nearly 

 conforms to that shown in PI. LXXX, fig. 6. That is from an older allied form, 

 and shows an isosceloid terminal lobule. That suture-line, however, does not 

 agree with what is stated above (No. 2), for that reason ; but it is of a pattern 

 like that of fig. 34. There is every possibility of both these developing asym- 

 metry like fig. 35 ; and therefore the word " become " has been used above, 

 at |3. It is the aim of this scheme to avoid the common error of grouping 

 morphic equivalents; its object is to bring together the species which are 

 assumed to be genetically connected, and to use as differentials the points 

 wherein they diverge from their neighbours during phyletic development. 



