172 Annals of the South African Museum. 



during the fifth whorl. At the middle zone, and below, the whorl is 

 evenly convex in outline. 



The shell-wall is thick. The surface of the whorls is marked by 

 numerous distinct, transverse growth-lines, which, however, do not 

 form an obtrusive feature. The spiral angle is about 90. The 

 inner lip of the aperture is considerably thickened and forms a raised 

 callus which bounds a well-impressed though closed umbilical slit. 

 Just below this, and adjacent to the inner lip, the surface of the 

 whorl presents a narrow, slightly flattened space. The height of the 

 aperture is much greater than the breadth. 



Dimensions. (1) (2) 



Height of shell 15 . 30mm. 



Height of body- whorl at the aperture 11 . 24 ,, 

 Greatest width at aperture 8 . 12 ,, 



Occurrence. Two well-preserved specimens in the collection of 

 the Geological Society of London are labelled " Zwartkop, Dr. 

 Atherstone, 1876." A specimen from the railway cutting between 

 milestones 24^ 24f on the railway from Uitenhage to Graaff-Eeinet, 

 about three miles from Uitenhage (350), is referred with some doubt 

 to the same species. 



Remarks. The specimen from the railway cutting (350) may per- 

 haps be identical with Atherstone's two individuals, upon which this 

 species is founded. It differs from them by its rather lower spire 

 and slightly wider spiral angle, and by the more complete overlapping 

 of the whorls. These differences may, however, be due to individual 

 variation. 



Natica atherstoni Sharpe, :;: another Uitenhage shell, is distin- 

 guished by its much more slender and elongated figure and narrow 

 apical angle (75). 



Compared at similar dimensions, Natica Icevigata (Desh.) Leym.,f 

 a Lower Cretaceous form, has much less overlap of the whorls, and 

 consequently a higher spire and narrower spiral angle. N. dupini 

 (Desh.) Leym.4 on the other hand, has a shorter spire and wider 

 spiral angle, with wider and more inflated whorls and less elongated 

 mouth aperture. The shell figured by d'Orbigny as N. dupini 

 shows much greater similarity to N. uitenliagensis, but this too has 

 a wider spiral angle and a broader aperture as well as a distinct 

 umbilical opening. 



* Sharpe (1), p. 200, pi. xxviii., fig. 22. 



f Leymerie (2), p. 13, pi. 16, fig. 10. 



J Leymerie (2), p. 13, pi. 16, fig. 7. 



d'Orbigny (2), p. 158, pi. 173, figs. 5, 6 (1843). 



