On Cretaceous Cephalopoda from Zululand. 251 



a reverse curve that is strongly convex forwards. A somewhat 

 similar costation is shown on the upper whorl-surface of D. pauper. 

 Whitfield sp.,* and of D. ? cunradi, Morton sp., in Whitfield.f 



The elongated tubercles, situated at each side of the siphonal zone 

 (which latter becomes almost smooth towards the end of the shell) are 

 small on the septate portion, but 4 mm. high and very sharp, where 

 preserved on the last whorl. There is only one uutuberculate inter- 

 mediate rib here and there, as on the last whorl of D. ? stevensoni, but 

 the bituberculation is rather irregular as regards spacing. 



The suture line shows good agreement with that of Didymoceras 

 tortum, Meek sp.,J except that the latter, taken at a larger diameter, 

 shows correspondingly greater complication. There is the same high 

 external lobe ; only in the present form the siphoual line lies between 

 the two rows of tubercles, which are placed more centrally. The 

 principal lateral lobe shows a similar smaller outer and larger inner 

 branch ; the lateral saddle is equally bifid, the smaller second lateral 

 lobe is bifid in the two forms, and the arrangement of the dorsal lobe 

 and saddles is very similar. In D. ? stevensoni, the very complex 

 suture-line, taken at a much larger diameter, shows a different deve- 

 lopment of the principal lobe, the outer branch being the larger. 

 The suture-line of D. pauper (Whitfield) also is very similar to that 

 here figured, and the whorl- section agrees, but the costation is 

 different. 



D. hornbyense, Whiteaves sp., a form somewhat resembling D. { 

 binodosum, Hauer sp.,|| is much more finely costate than the specimen 

 here described, to judge by an example from Vancouver Island in the 

 British Museum,^ and other specimens of Didymoceras in the same 

 collection from the Upper Missouri, etc., differ in the same respect. 



* Loc. cit. (1892), pi. xlv, fig. 3. 



f Ibid., pi. xlv, fig. 10. 



I Loc. cit. (1876), p. 481, pi. xxii, fig. 4 c. 



Loc. cit. (Mesoz. Foss. I), p. 332, pi. xlii, figs. 1-4. 



|| " Neue Ceph. a. d. Gosaugeb. d. Alp.," ' Sitz. B. K. Akad. Wiss.,' vol. liii 

 (1866), p. 8, pi. i, fig. 6. This, however, may be a Bostrychoceras. 



f This was labelled by Kossmat " Heteroceras sp. aff. cooperi, Meek," whereas 

 another example of a Didymoceras, corresponding somewhat to Whiteaves' A. 

 cooperi (loc. cit., pi. xliii, fig. 1), but not with Meek's specimen or Gabb's fragment 

 (the latter compared with Emperoceras by Hyatt, loc. cit., p. 576), was wrongly 

 labelled by Kossmat " Acanthoceras vancouvrensis, Meek." In form and costa- 

 tion this second fragment recalls D. ? conradi (Morton), Whitfield sp., and 

 Emperoceras simplicostalum, Whitfield sp., but there is also a striking resem- 

 blance of the looped tubercles with the ornament of Jacolites anderssoni, Kilian 

 and Reboul (loc, cit., 1909, p. 35, pi. viii, fig. 3). 



