On Cretaceous Cephalopoda from Zululand. 279 



Ammonite is distinguished from the true D. bouchardianum, d'Orbigny,* 

 by its evolute and square whorls, with a wide, carinati-sulcate ventral 

 area. It may be considered to form a transition towards the sub- 

 cristatttm and subinflatum groups, as d'Orbiguy's compressed type has 

 leanings towards Pseudopliacoceras roissyanum, d'Orbigiiy sp. The 

 resemblance of Pictet's example to I). subcristatum consists chiefly of 

 the peculiar trifurcation of some of the costae ; whereas in the smaller 

 Zululand specimen, comparable with the inner whorls of Pictet's 

 form, this resemblance is due to the slightly greater prominence of one 

 or two of the costae, though there are no conspicuous flares, such as 

 are characteristic of the cristatum group. 



The present example, on the other hand, does not show the umbilical 

 tuberculation that is so notable a feature in Pictet's much larger 



c? 



specimen, but, as in d'Orbigny's species, a pair of costae may be 

 thickened where they meet at the umbilicus. The example, perhaps, 

 might be thought to represent only the inner whorls of a large 

 specimen, such as Boule, Lenioine and Theveuin's " Schloenbachia cf. 

 boucliardiana?^ It appears probable, however, that the last half- 

 whorl, at least, of the present example belongs to the body-chamber, 

 though the suture-line, unfortunately, cannot be made out. 



The Madagascar specimen, referred to above, which is larger than 

 any European form of this group, and therefore difficult to compare, 

 apparently does not agree either with d'Orbigny's species or with the 

 species here discussed, and may represent a new type. In D. sub- 

 inflatum, Pictet sp.,J and in D. rouxianutn, Pictet sp., the umbilical 

 tuberculation is far too pronounced. 



Forms comparable with the present species, but not with d'Orbigny's 

 form, are found in bed VIII at Folkestone, but in the succeeding 

 zones, forms belonging to the group of Brancoceras symmetricum , 

 Sowerby sp., are common, and often confused with D. bouchar- 

 dianum.\\ Other transitional forms of Dipoloceras from the cristatus 

 zone of Folkestone differ from the present species in having the point, 

 of bifurcation of the costae moved farther away from the umbilicus. 



Locality. Middle Branch, Manuau Creek. Coll. W. J. Wybergh. 



* Luc. eft. (1840), p. 301, pi. Ixxxviii, figs. 6-8. 



t Loc. cif. (1907, ii), p. 39, pi. ix, fig. 11. 



j In Pictet and Boxix, loc. clt. (1847), p. 104, pi. x, fig. 1. A specimen in the 

 British Museum, also from Mt. Saxonet (No. C. 10399) forms a transition to 

 Rrancoceras symmetricum (Sow.). 



Ibid., p. 99, pi. ix, figs. 2 a, b. 



|| See Price, "On the Gault of Folkestone," 'Q.J.G.S.,' vol. xxx (1874), table 

 on p. 362 ; and Jukes-Browne and Hill, ' Cret. Eocks Britain,' I, " Gault and 

 Up. Gr. Sd. of Engl.," tables on pp. 82 and 459. 



