SONNINIA CRASSIFORMIS. 401 



In external shape Sonn. inaequa has much resemblance to Sonn. costata; but it 

 differs from the form of that species in being so much less costate, and in having 

 a less angular, more rounded ventral area. Internally, in septation it differs con- 

 siderably — the superior lateral lobe is more asymmetrical, the terminal lobule is 

 far more anisosceloid, the lateral lobules are anisometric. There is a certain like- 

 ness in septation to Sonn. crassibullata — the inner lobule in both species is, in a 

 sense, double, a feature which is peculiar to these two forms. In other characters 

 they do not at all show that agreement which direct genetic relationship would 

 produce. 



Mr. B. Wilson, F.G.S., kindly gave me the figured specimen which he recently 

 obtained from Stoke Knap, near Broad Windsor, Dorset. A specimen from 

 Bradford Abbas, which agrees with this in the feeble costation, in the septation, and 

 in the matter of the arched periphery — and had in consequence of these features 

 been separated from Sonn. costata — must evidently be placed with the present 

 species, though it is the least trifle thicker. It shows a quarter-whorl body- 

 chamber, and attains the diameter of 190 mm. 



Outer lateral lobule in duplicate. 



Fig. 37. — Outline of L of Sonn. crassiformis. 



1. Lobes long and ornate. 



Sonninia crassiformis, S. Buckman. See Plate LXXIX, figs. 1 — 6, and page 348. 



In this species there are two outer lateral lobules to L (PI. LXXIX, fig. 6) ; in 

 other words the outer lobule is cleft to its base. In Sonn. crassa the outer 

 lobule is only cleft about half way. 



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