The Invertebrate Fauna oj the Uitcnhage Scries. 191 



ribbed, and though the ribs seemed most crowded in the specimen 

 referred by M. Kilian to H. sayni, yet the differences in this respect 

 did not appear to me to be at all considerable, and other points of 

 distinction, such as the more discoidal form, were probably to be 

 accounted for by distortion through crushing. A comparison of 

 these specimens with Sharpe's type, and other examples of 

 H. atJierstoni, shows that in H. atherstoni the shell is much more 

 inflated and less discoidal : the whorl is broader in section and less 

 highly arched. The umbilicus is relatively much narrower and 

 more profound. The umbilical wall falls more abruptly and steeply 

 into the umbilical cavity. The involution is greater. In the French 

 specimens the umbilicus is of a broader and shallower type, and the 

 involution is such that the tubercles, together with part of the ribbing 

 of the flank, are visible in the penultimate whorl. The involution, 

 in fact, is less than in the last whorl of the considerably larger type- 

 specimen of H. atherstoni. The primary (umbilical) ribs are also 

 much more weakly developed than in H. atJierstoni. The ribbing of 

 the flank and periphery of H. atJierstoni is of a somewhat coarser 

 type, and the ribs are rather more prominent and are less closely 

 crowded together than those of the French specimens. At a selected 

 stage of growth comparable in the two forms, a space of 20 mm. 

 along the periphery includes 9 ribs in H. atherstoni and 13 in the 

 French shells. In H. sayni an occasional bifurcation of a rib, or 

 the intercalation of a shorter rib between two longer ones, may be 

 observed to occur on the flank at a varying but usually considerable 

 distance away from the tubercles. In H. atherstoni, the ribs of the 

 flank all have their commencement either at, or in the near vicinity 

 of, the tubercles, and bifurcation of the ribs has not been observed 

 on any part of the flank. 



It is clear, therefore, that these French specimens are not very 

 closely comparable with H. atherstoni, and I think it highly probable 

 that all three represent H. sayni Kilian," a finely ribbed species very 

 nearly allied to H. astierianus (d'Orb.). 



A specimen from the Neocomian of Speeton (zone of Belemnites 

 jaculum), preserved in the Scarborough Museum, was figured by 

 Pavlow (Bull. Soc. Imp. Nat. Mosc., 1892, pi. xvii., fig. 14) and con- 

 sidered by him to be identical with H. atherstoni. Through the 

 kindness of Mr. H. Ascough Chapman and Mr. J. A. Hargreaves, of 

 Scarborough, I have been able to compare this Yorkshire individual 

 with Sharpe's type and other examples of H. atherstoni from South 



* Kilian and Leenhardt (1), p. 976 ; Sarasin and Schondelmayer (1), part 1, p. 38, 

 pi. iv., figs. 2, 3 ; d'Orbigny (1), pi. 28, fig. 4. 



