196 Annals of the South African Museum. 



Occurrence. The specimen is in the collection of the Geological 

 Society of London (registered 10975A), and the label affixed to it 

 bears the following record of locality and collector : " Aasvogel 

 Krantz above Modder Drift, Sunday's Eiver, S. Africa. Dr. 

 Atherstone, F.G.S., 1876." 



Remarks. The individual above described is almost complete, 

 comprising the body-chamber, but the exact length of this cannot be 

 ascertained, nor is the shell so preserved that the lobe-line is any- 

 where visible. The specimen has undergone some distortion from 

 crushing, but making every allowance for this, it is clear that we are 

 dealing with a form well distinguished by its high whorl-section and 

 extensive flattened flanks. In the discoidal form, the relatively 

 shallow umbilicus, and the degree of involution, we are reminded of 

 H. astierianus (d'Orb.),* but H. wilmance is readily separated from 

 this by its very strong, oblique umbilical ribs and tubercles, and by 

 the inclination and the coarseness of the secondary costae. 



This appears to be the specimen mentioned by Pavlow f as a 

 compressed variety of H. atherstoni, but it was recognised that 

 the distinctive characters are sufficient to warrant a new specific 

 name (op. cit. p. 492). As pointed out by Pavlow, the specimen 

 is distinguished from the typical H. atherstoni by the presence 

 of rather fewer umbilical ribs and by the more strongly developed 

 secondary costse. In addition, H. atherstoni is a considerably 

 more strongly inflated shell, and has a relatively narrower and 

 much more profound umbilicus. The points of distinction are in 

 fact so great that the only course open is to definitely separate 

 the two forms. 



There is much stronger resemblance to H. psilostomus Neum. and 

 Uhlig4 from the Neocomian of North Germany. The ribbing is of 

 very similar character, but in H. psilostomus the umbilical ribs are 

 rather more numerous, the breadth of the umbilicus is somewhat 

 greater relatively to that of the flank, and the shell, although much 

 more laterally compressed than H. atherstoni, is still considerably 

 more inflated and less discoidal than in H. wilmance. I believe that 

 the presence of the above characters of distinction must be con- 

 sidered sufficient to warrant the provisional separation of these two 

 forms, but there can be little doubt that the relationship is intimate, 

 and there is no other known Holcostephanus with which H.ioilmana 

 can be brought into such close comparison. 



* d'Orbigny (1), p. 115, pi. 28, fig. 1 (1840). 



f Pavlow and Lamplugh (1), p. 496 (p. 138 of authors' copy). 



} Neumayr and Uhlig (1), p. 149, Taf. xxxii., fig. 2. 



