166 Annals of the South African Museum. 



the features of T. baini are exhibited. The change in characters is 

 found to be very constant, although some slight variation may be 

 shown as regards the exact period, in relation to the precise number 

 of whorls developed, when the additional keel makes its appearance. 

 In this connection also, differences of preservation prove very decep- 

 tive. As the adult stage becomes completed, it is noticeable how 

 relatively rapidly, by the greater expansion of the whorls, the shell 

 gains in length when compared with the proportional dimensions of 

 the young individual. 



This well- characterised form seems to resemble very closely Turbo 

 reedi W. Keeping," 1 ' from the Lower Cretaceous of England, and may 

 be more aptly compared with this than with any other European 

 shell with which I am acquainted. The type of ornamentation is 

 essentially similar as regards major features, and while Keeping 

 gave no account of the variation of sculptural characters when 

 traced through successive stages, it seems probable that the central 

 marginal keel became added between the two prominent keels during 

 the course of individual growth, just as in T. atherstoni. The 

 principal points by which the English shell differs, are seen in the 

 greater number of spiral ribs on the lower part of the body-whorl 

 and in the very delicate spiral striation and resulting granulation of 

 the surface. 



A somewhat analogous type of ornamentation is exhibited by a 

 shell from the Upper Neocomian of Utrillas (Teruel), described as a 

 Trochus, under the name T. maestrei, by de Verneuil and Loriere. f 

 This, however, shows only two marginal spiral keels, while the base 

 of the body-whorl is ornamented by several strong, well-spaced 

 keels. Further points of distinction are the fine spiral lines which 

 ornament the whorls, and the wider spiral angle. 



A form which perhaps merits mention by way of comparison 

 occurs in the Upper Jurassic Aucella-beds of Novaya Zemlya, and 

 was ascribed by Tullberg to Minister's Turbo capitaneus.\ This has 

 ornaments similar to those of T. atherstoni, but there is less overlap 

 of the whorls, the upper and lower marginal keels are less 

 prominent and of similar strength to the central one, and the 

 outline of the whorl is more rounded and less angular. There are 

 apparently other differences, so far as it is possible to make com- 

 parison with the figure of the relatively large specimen figured by 

 Tullberg. 



* Keeping (1), p. 97, pi. iii., fig. 13. 



f de Verneuil and Loriere (1), p. 23, pi. ii., fig. 9. 



t Tullberg (1), p. 9, pi. ii., fig. 1. 



