202 Annals of the South African Museum. 



Remarks. Although I have only seen a single specimen, and 

 the state of preservation of this is not so good as might be desired, 

 I have no hesitation in pronouncing it to represent a hitherto 

 undescribed form. It is apparent that though distinctively charac- 

 terised, particularly by the feature of reclined costation, this 

 ammonite may be brought into closest relationship with H. baini 

 (Sharpe) and H. schenki (Oppel), and particularly with the latter. 

 H. baini has the whorl relatively narrower and more highly arched 

 in section, while its ribbing is noticeably coarser. On the peri- 

 pheral part of the whorl at a comparable stage there are seven ribs 

 in H. rogersi within a space which includes only six ribs in 

 H. baini. Moreover, the ribs in H. baini have a marked forward 

 inclination as they depart from the nodes. 



Eeference to the published descriptions and figures of H. schenki," 

 from Shangra, east of Puling (Tibet), seemed to show a very close 

 resemblance between the two forms, but I have been able to 

 supplement this by an actual comparison with Oppel's type- 

 specimen in the State Palaeontological Collection at Munich, and 

 when making this comparison I was fortunate in having the kind 

 assistance of Prof. J. F. Pompeckj. H. schenki has rather more 

 numerous umbilical tubercles and is slightly more densely ribbed 

 than H. rogersi. In H. schenki the umbilicus is relatively a little 

 wider and in cross-section the whorl is rather wider between the 

 umbilical rims, in relation to the height. The most notable point 

 of distinction, however, is in the course taken by the secondary 

 ribs as they pass from the tubercles over the periphery. In 

 H. schenki they have a forward inclination, while in H. rogersi they 

 are slightly reclined. 



There is considerable resemblance between H. rogersi and H. 

 guebhardi Kilian, i from the Hauterivian of the neighbourhood of 

 Escragnolles in the Maritime Alps, but in H. guebhardi the ribbing 

 of the flank is strictly radial in direction. 



HOLCOSTEPHANUS MODDEKENSIS Sp. nOV 



Plate X., figs 3, 3a. 



1892. Astieria schenki A. P. Pavlow (partim), Bull. Soc. Imp. Nat. 



Mosc., annee 1891, Nouv. Ser., tome v., p. 493 (p. 135 



of authors' copy). 



Description of a Single Specimen. The shell has rapidly expanding 

 whorls, and is involute to the umbilical marginal tubercles in the 



* Oppel (2), p. 286, Tab. 81, figs. 4a-c ; Uhlig (4), p. 130, pi. xviii., figs. 2a-c. 

 j- Kilian (4), p. 866, pi. Ivii., figs. 2a, 2b. 



