194 Annals of the South African Museum. 



Greatest height of the last whorl at the centre, in section 35 mm. 

 Greatest diameter of the umbilicus, measured from the 



umbilical rim between the tubercles 48 ,, 



In the type-specimen of H. atherstoni the maximum diameter is 

 140 mm., the greatest breadth of the last whorl 90 mm., and the 

 height of the last whorl in section at its anterior part 42 mm. It is 

 thus seen that the height of the whorl-section in relation to its 

 breadth is somewhat different. In the more inflated specimen, when 

 the breadth of the whorl is 86 mm. its height at the centre is 32 mm. ; 

 in H. atherstoni (type-specimen) I have estimated that with a 

 breadth of 86 mm. the height is 40 mm. The two left-hand 

 specimens, depicted in greatly reduced size, in a text-figure pub- 

 lished by Drs. Hatch and Corstorphine,* may perhaps represent this 

 inflated form. 



Mr. G. C. Crick has shown me a specimen in the British Museum 

 (registered 46534) which closely agrees with the one here discussed. 

 It is from the Sunday's Eiver (from A. G. Bain's collection), and has 

 at some time been determined as Olcostephanus atherstoni. It has 

 an inflated form and breadth of whorl-section which seem to dis- 

 tinguish it from H. atherstoni, as exemplified by Sharpe's figured 

 type, in the manner described above in the case of the other 

 specimen. The greatest diameter of this individual in the British 

 Museum is 145 mm. The greatest breadth of the ultimate whorl 

 would, when complete, have been almost 100 mm., while the height 

 of this whorl at the centre at its anterior end would have slightly ex- 

 ceeded 35 mm. In the breadth of the umbilicus and in all other 

 characters there is the closest agreement with the specimen from the 

 South African Museum. This would seem to indicate that fixed and 

 reliable characters are exhibited which may suffice to separate this 

 more globose shell from the true H. atherstoni, and it might perhaps 

 be possible to establish the constancy of these distinctive features 

 were a suite of specimens of undoubted H. atherstoni, at a suitable 

 stage of growth, available for comparison. Unfortunately this is not 

 the case, and the only specimen of H. atherstoni that I have seen 

 which illustrates a comparable stage is Sharpe's figured type. Com- 

 parison with this has revealed the slight shape differences above 

 noted, but beyond this there is entire agreement ; the characteristic 

 ornamentation, the degree of involution and the width of the 

 umbilicus are the same. There is as yet no material for a 

 comparison of the septal sutures. I therefore do not yet feel 

 justified in proposing a new specific name for the specimens here 

 * Hatch and Corstorphine (1), p. 243, fig. 65 (as Olcostephanus bainii). 



