416 INFERIOR OOLITE AMMONITES. 



spined period. Whorl-section elliptical. Suture-line with rather long, thin- 

 stemmed lobes, not strongly branched ; L carrying on its inside several minor 

 lobules, the inner lateral lobule being small ; terminal lobule intra-axial, anisos- 

 celoid ; lateral lobules anisometric, short. 



The paired ribs are similar to what obtains in 8. biplicata and 8. alternata ; 

 but from both of these the present species is distinguished by its septation. 

 Further, it is less gibbous-whorled, less ornate, and less spinous than the first ; 

 more umbilicate and differently costate to the second. 



Sown, plicata is a rare fossil in the Concavum-zone of Bradford Abbas. It is 

 figured in PI. XCVII : fig. 6, side view, and fig. 7, front view, both reduced to two- 

 thirds natural size ; fig. 8, the septa. 



Sonninia semispinata, 8. Buchnan. Plate CIII, fig. 15. 

 See Plate LXXVII, figs. 1, 2, and page 343. 



Add to description : — Septa with fairly long but brevilobulate lobes, L with 

 terminal lobule intra-axial, anisosceloid ; lateral lobules short, inner lateral lobule 

 much abbreviated and rudimentary, outer lobule slightly bipartite. 



The septa prevent this species being included in the magnispinata-stock, which 

 the external features seem to warrant (p. 341) ; and they cause its association 

 with Sonn. plicata. They do not quite agree with the suture-line of that species, 

 but they show considerable similarity. External features show little likeness to 

 plicata ; there is hardly that similarity even which might suggest genetic 

 connection between the two forms. 



•y. Lateral lobules rather long, outer bipartite. 



Fig. 45. — Outline of L of Sonn. revirescens. 



