280 Annals of the South African Museum. 



6. DIPOLOCERAS sp. nov. 

 (PL XXVI, figs. 5 a, ft.) 



Of. 1910. Schloenbachia n. sp. Bose, " Mon. Geol. & Pal. d. Cerro 



de Muleros," Bol. lust. Geol. Mexico, No. 25, p. 74, pi. viii, fig. 6. 

 The fragment (No. 4903) to be described, unfortunately, is too 

 incomplete to justify the creation of a new species, but the characters 

 of the body-chamber, as well as of what is preserved of the inner 

 whorls, clearly distinguish it from the previously described forms of 

 this group. The measurements, based on the restoration of the 

 complete shell, shown in fig. 5 a, are : 



Diameter . . 39 mm. 



Height of the last whorl . 46 per cent, of the diameter 

 Thickness ,, 35 



Umbilicus ,, ,, . 22 ,, ,, 



Except for the smaller umbilicus of the present example, these 

 measurements agree with those of D. sergipense, White sp.* There is 

 a similar strong outer tubercle and high keel, but the latter, in the 

 Zululand specimen, is of the shape of that of A. roissyanus (d'Orbigny) 

 varietas, Ooster,t or of many specimens of Dipoloceras cristatum, that 

 are well enough preserved that is to say, it is thinner at its base than 

 at its middle height, and becomes thin and sharp again at the edge. 

 But the present species has a second small tubercle half way between 

 the much more prominent outer tubercle and the umbilical suture. 

 Similar bituberculation is shown in some varieties of D. (Mojsisovicsia ?) 

 delaruei, d'Orbigny sp., e . g. the form figured by Parona and Bonarelli,+ 

 only in the present species it is more developed, and altogether the 

 new form, like Mojsisovicsia ventanillensis, Gabb sp., shows a decided 

 resemblance to the later Subschloenbachia. Of the bituberculate forms 

 included by Bose in " Schloenbachia n. sp.," his figs. 6-8, pi. viii, 

 represent a closely comparable form ; but the inner tubercle is hardly 

 indicated, whereas in figs. 4 and 5 it is the outer tubercle that is not 

 prominent enough. Besides, both these examples are represented as 

 having an acute periphery instead of a high keel on a fiat periphery, 

 such as is characteristic of D. sergipense and the delaruei group. 



* "Contrib. Pal. Brazil," 'Arch. Mus. Nac. Rio de Janeiro,' vol. vii (1887), 

 p. 221, pi xxiv, figs. 1 and 2. A specimen intermediate between this species 

 and D. (Mojsisovicsia ?) delaruei (d'Orbigny) in the British Museum (No. C4255), 

 from Velez, Colombia, with a smaller umbilicixs, is still nearer to the present 

 example, and also shows the steep forward edge of the costae very well. 



t ' Catal. Ceph. Foss./ etc., 1860, iv, p. 144, pi. xxvi, figs. 6 and 7. 



J " Foss. Alb. d'Escragnolles," ' Pal. Ital.,' vol. ii (1896), p. 88, pi. xi,fig. 9 only. 



