422 INFERIOR OOLITE AMMONITES. 



area rounded, divided by a fair-sized hollow carina. Inner margin ill-defined, 

 nearly upright. Inclusion about one-third, but not up to the spines except in the 

 central whorls. Umbilicus with a regular spinous stage in the central whorls, 1 

 very soon yielding to an irregular spinous stage. Whorl-section gibbous- 

 sided, oval. Suture-line 2 with rather long, narrow-stemmed lobes : the terminal 

 lobule of L intra-axial, anisosceloid, inequicellate ; the lateral lobules, which are at 

 first isometric, and not opposite, become with age very anisometric, the inner 

 lobule being practically aborted. 



In septation this form agrees, when young, with Sonn. reclinans, and it is not 

 difficult to imagine it a descendant thereof ; it is in part distinguished by being 

 more quickly coiled, broader whorled, and more coarsely ornamented, — all these 

 might be features of development. It also has resemblance to Sonn. acanthodes and 

 Sonn. irregularis, but it is more quickly coiled and less spinous than the first, 

 has more gibbous sides, few and smaller spines, and different septation from the 

 second. 



A remarkable feature which this form exhibits is the abortion of the inner 

 lateral lobule of L, shown by the septa of the same specimen at different ages. 



Sonn. gibbera occurs in the Concavum-zone of Bradford Abbas. The type- 

 specimen is figured in PI. LXXXVII : fig. 4 side view, fig. 5 front view reduced to 

 two-thirds of natural size. In PI. LXXXVIII, fig. 1 gives the septa from another 

 specimen, and figs. 2 and 3 part of the suture-lines from yet another example. 



Sonninia modesta, S. Buckman. Plate XCV, figs. 3 — 5; Plate XCVI, figs. 1,2. 

 See Plate LXX, fig. 5, and page 325 ; also ? abnormal form, Plate 

 LXVIII, and its septa, Plate CIII, fig. 5. 



It has been considered advisable to figure the actual type of this species when 

 it was found that there was a considerable difference in septation between it and 

 the presumably abnormal form (PI. LXVIII). The septa of the type have been 

 drawn again, more matrix having successfully been removed, and they show 

 much complexity, L having a terminal lobule very intra-axial, very anisosceloid 

 and inequicellate, and the lateral lobules very anisometric, the outer lobule being 

 strongly bipartite, almost tripartite. The species just described seemed to indicate 

 that such features as these would be the outcome of their phyletic development. 



1 Detail from another specimen. 



2 From other examples. 



