SONNINIA UMBILICATA. 397 



Sonninia umbilicata, 8. Buckman. Plate LXXXIV, figs. 1 —3. 



Discoidal, compressed, carinate. Whorls ornamented with direct, not very 

 conspicuous, nearly upright, ventrally-inclined (almost ventrally-projected) costse. 

 Ventral area rounded, divided by a small carina. Inner margin fairly defined, 

 sloping. Umbilicus open, ornamented with ribs, no spinous stage being discernible. 

 Whorl-section oblong. Suture-line simple with a superior lateral lobe of moderate 

 length, the lateral lobules anisometric, the terminal lobule slightly intra-axial, 

 isosceloid, scarcely equicellate. 



This form is like Sonn. parvicostata. It has, however, a flatter, larger umbilicus, 

 more compressed whorls, and more pronounced costation. Its suture-line agrees 

 fairly with that of Sonn. parvicostata, except that the lateral lobules of the superior 

 lateral lobe are somewhat more anisometric. The various points of similarity 

 detailed above suggest the position of this species. 



From Sonn. omphalica the septation, and the want of spines 1 distinguish this 

 species ; it has also more compressed whorls and smaller ribs. The septation 

 negatives any idea of genetic connection between S. umbilicata and S. omphalica ; 

 but the other features would not — in fact, they rather suggest it. 



Sonn. umbilicata is from the Goncavum-zone of Bradford Abbas, Dorset. 



Side view, front view, and suture-line are illustrated in PL LXXXIV, figs. 1 — 3. 

 The specimen is possessed of test. 



j3. Lateral lobules become distinctly anisometric. 

 1. Terminal lobule isosceloid. 



Fig. 34. — Outline of L of Sonn. crassa. 



1 It is reasonable to assume a spinous stage in the innermost whorls, but it must have ended 

 very early. 



