230 Ann al# <>/ the South African Museum. 



A gigantic example (No. 3969) resembles the form last described,, 

 but has a wider umbilicus. Its dimensions are : 

 Diameter - . 390 mm. 



Height of the last whorl . . 46 per cent, of the diameter. 

 Thickness ,, ,, . 49 



Umbilicus .... 25 



The costatioii disappears on the ventral area and remains distinct on 

 the inner half of the side, which is just the reverse of what takes 

 place in P. supremus, Petho sp.,* included in the synonymy of 

 P. enlligaius, Binkhorst sp., by G-rossouvre and Nowak.f P. 

 f'rt'xrHlrHsis, Seunes,J and P. epiplectus, Redtenbacher, show a similar 

 change, but one of the examples of the former species, figured by 

 Seunes (pi. xii (iii), fig. 1), agrees with the specimen here described in 

 having a somewhat reniform whorl-section, with the greatest thickness 

 near the umbilical border. The latter character distinguishes the 

 Zululand example from P. teshionensis, Jimbo,|| which apparently 

 weakens the ornament of the periphery and retains the principal 

 lateral costae after the manner of P. ecjertonianus (Forbes), Stoliczka 

 sp.,^~ which latter species, however, is far too compressed. 



P. haradai, Jimbo,** and the larger example referred to the same 

 species by Whiteaves,ft have more compressed whorls at a stage when 

 the present form is still very depressed. It is also doubtful whether 

 large examples of this species would develop the secondary ornamenta- 

 tion of the typical forms of this group. This equally applies to the 

 evolute P. steinmanni, Paulcke,++ that may or may not develop these 

 obscure bulges at a large diameter, but resembles the form here 

 described in the roundness of the inner whorls. 



Schliiter's A. wittekindi differs from the form here described in 

 whorl-section, though the inner whorls of the South African form 

 apparently are more depressed than is its outer whorl. The West- 

 phalian form also appears to lose its first costatioii at an earlier stage, 



* " Kreidefauna d. Peterwardeiner Geb.," 'Palaeontogr.,' vol. Iii (1906), p. 88, 

 pi. v, fig. 1. 



t Loc. cit. (1908), p. 29 and (1913) p. 361. 



I "Contrib. a 1'Et. d. Cephal. Cret, Sup. France," ' Mem. Soc. Geol. Fr.,' Pal.,. 

 vol. ii, fasc. iii (1891), p. 3, pi. i, fig. 1. 



Loc. cit., p. 121, pi. xxviii, fig. 1. 

 i Loc. cit. (1894), p. 30 (176), pi. iii, fig. 1. 



^ Loc. cit. (1865), p. 104, pi. liii, fig. 1. 



** Loc. cit. (1894), p. 29, pi. ii, fig. 2. 



ft "Vancouver Cret, Foss.," 'Trans. Roy. Soc. Can.,' 2nd ser., vol. i (1895),, 

 sect, iv, 1896, p. 132, pi. iii, fig. 6. 



H Loc. cit. (1907), p. 230 (64), pi. xviii (ix), fig. 1. 



