404 INFERIOR OOLITE AMMONITES. 



Partly on account of the considerable reduction, the figure does not fully 

 show this peculiar curvature of the last quarter of the ultimate whorl, yet both 

 the periphery and the inner margin have a decided bend at about 120 mm. shell- 

 radius. Another specimen, 160 mm. in diameter, shows a similar bend at about 

 95 mm. shell-radius. It commences to enlarge its costse rather earlier than the 

 type, namely, at about 145 mm. diameter. This is the specimen which has 

 furnished the suture-line. 



The correlation of an increase in umbilication and costation in the gerontic 

 stage of a phylogerontic species is interesting as showing a combination of 

 features which usually belong to the commencement of a genetic cycle. Their 

 occurrence in the present case seems to indicate a tendency to a recommence- 

 ment of the cycle in the phylogerontic stage. As the increase in umbilication 

 is connected with a narrowing of the whorl and no corresponding increase in 

 thickness, this apparent renewal of progressive development is plainly degenera- 

 tive, and may be considered in a sense pathological. 



Sonninia camura occurs in the Concavum-zone of Bradford Abbas, but is some- 

 what scarce. The side view (PI. XCIX, fig. 4) is considerably reduced ; it is a 

 copy from a photograph, and is - x % of the original. The outline of the whorl- 

 section (fig. 5) is of natural size ; the suture-line (fig. 6) is from another specimen. 



II. The terminal lobule of L is intra-axial in the spinous species, and generally 

 anisosceloid. 

 A. The lobes and lobules are short and broad-stemmed. 



Fig. 38. — Outline of L of Sonn. spinea. 



A. These characters are well marked, 

 a. Costation irregular. 



Sonninia abnormis, S. Buchman. See Plate LXXXV, figs. 4 — 6, and page 377. 



