The Invertebrate Fauna of the Uitenhage Series. 165 



prominently projecting longitudinal (spiral) keel limiting the trun- 

 cated band above, and also a similar one below. Under the lower 

 marginal keel the surface of the whorl is gently convex in profile and 

 slopes rapidly in. Just below the lower marginal keel there is a 

 narrow, deep spiral sulcus bounded below by a delicate thread-like 

 longitudinal keel. Below this there are four weaker raised spiral 

 lines which are already developed in the third whorl, if not before. 

 Until the fourth whorl is reached, the slightly concave outer band 

 between the prominent marginal keels is smooth, but before this 

 whorl is completed, in some individuals at its commencement, a 

 weaker central keel appears. 



The spiral angle varies somewhat, and averages about 70. The 

 last two whorls expand rapidly. The spiral suture is situated on the 

 lower marginal keel of the whorls. The mouth has an angular 

 outer lip, corresponding with the form of the whorls. The outer 

 margin of the aperture is thin and sharp ; under the columella the 

 margin is slightly thickened. 



Dimensions. 



I Height of a specimen with four complete whorls 5 mm. 



I Diameter of the fourth whorl 4 ,, 



( Height of a specimen with five (or six ?) whorls 14 ,, 

 I Diameter of the body- whorl 9 ,, 



Occurrence. Found in the cliff below the old school-house at 

 Dunbrodie on the Sunday's Eiver (351), where it is abundant. 

 Specimens in the collection of the Geological Society of London are 

 from "the lowest strata of the Zwartkop crag," and "greenish grit 

 with Ostrece from Sunday Eiver," as recorded by Sharpe. This form 

 was obtained by Mr. Eogers in 1905 in a cliff W. 20 S. from Comley's 

 house, right bank of Sunday's Eiver (95h). 



Remarks. It is clear from a careful examination of the specimens 

 in the collection of the Geological Society, together with the new 

 materials supplied to me, that Sharpe was in error when he separated 

 the shells described by him as Turbo atherstoni and T. baini. The 

 differences which caused him to make the separation are in reality 

 due to changes in the nature of the ornamentation during successive 

 stages of growth ; but the specimens at his disposal were very small 

 and the materials so comparatively unsatisfactory that the mistake 

 is not surprising. All specimens having the two marginal keels 

 only, and consequently agreeing with the type of T. atherstoni, are 

 very small individuals which have not reached the stage in which, by 

 the intercalation of a central marginal keel and the more prominent 

 development of the spiral ornaments on the lower part of the whorl, 



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