392 INFERIOR OOLITE AMMONITES. 



The above is the skeleton classification. The following pages give a more 

 detailed account of the species arranged on the same plan, with descriptions of 

 those which are new, and supplementary notes where necessary to those previously 

 described. The absence of a back reference will distinguish the new species. 



A detailed classification of the Sonninise of the Concavum-zone. 



I. The terminal lobule of L is axial in the spinous stage of the phyletic 

 series, and generally isosceloid. 



A. The terminal lobule remains axial during phyletic development. 



A. The lateral lobules equipoised, isometric, non-partite. 



Fig. 30. — Outline of L of Sonn. dominatrix. 



a. Costge strong. 



Sonninia dominatrix, 8. Buckman. Plate XCIV, figs. 3 and 4 ; Plate XCV, fig. 2. 

 1892. Sonninia dominans 8. This Monograph, p. 323. 



Discoidal, compressed, hollow- carinate. Whorls ornamented with direct, 

 nearly upright, ventrally-inclined, increasingly prominent, on the median area 

 subbullate costse. (A regular spinous stage to about 15 mm. shell-diameter ; 

 then a slightly irregular spinous stage to about 25 mm. shell-diameter, and for 

 about half a whorl further a stage with spinicostaa and costae as 1 to 2.) 

 Ventral area arched, somewhat flattened, divided by a small, rounded, fairly- 

 defined carina. Inner margin broad, well-defined, nearly upright, flat. Inclusion 

 about one-third. Umbilicus somewhat deep, regularly graduate. Whorl-section 

 gibbous-sided, oblong. Suture-line with short lobes ; L symmetrical, the terminal 

 lobule axial, isosceloid, equicellate ; the lateral lobules equipoised, isometric, non- 

 partite. 



From Sonn. dominans this form differs in being much more costate, and in 

 commencing the coarse distant ribs earlier in life. It has further a suture-line 

 with shorter lobes, and the superior lateral lobe more equally balanced — the 

 lateral lobules being practically isometric. This seems to be a not uncommon 

 form of the Bradford Abbas Goncavum-hed ; but then there are other species of 



