250 Annals of tie South African Museum. 



13. NOSTOCERAS ? SUBANGULATDM, Sp. UOV. 



(PL XXII, figs. 3 or-c.) 



A sinistrally coiled, fairly elevated but fragmentary turricone 

 (No. 2746A), consisting of just over two whorls of body-chamber and 

 of a small portion of the septate and possibly more loosely coiled 

 earlier whorls, is doubtfully referred to the genus Nostoceras. There 

 is great resemblance to the dextrally coiled Didymoceras ? stevensoni, 

 Whitfield sp.,* and the helicoid character of the earlier whorls, if 

 proved by the discovery of more perfect examples, may necessitate the 

 transfer of the new form to the genus Didymoceras ; on the other 

 hand, the beginning of the example here described already shows an 

 impressed zone of contact, so that the reference to Nostoceras seems 

 most proper. Like the species last described, the present example 

 with its strong, simple costation and double row of ventral tubercles 

 recalls the ornamentation of the genus Exiteloceras, and the fragment 

 of Ex. artfjulatnm figured by Meek,t shows a close resemblance to the 

 septate portion here described, though there is a considerable difference 

 in size. The openly helicoid or irregular coiling of the young of Evite- 

 loceras,% however, is quite distinct. 



The whorl-section is almost rounded, except for the double row of 

 tubercles on the ventral area, slightly below the middle, and the 

 impressed zone on the upper surface, indicating affinity with N. 

 stantoni and " IV. ? " cf. stevensoni (Whitfield) in Hyatt. The costation 

 is very irregular ; on the small septate portion, the costae have a very 

 steep forward edge and a gentle slope backward, and are continuous 

 between the slight tubercles. On the under-side they are projected 

 strongly forward, towards the umbilicus, as in the basal view of 

 Didymoceras? stert'itx<>n!, Whitfield sp.|j On the upper surface they 

 describe first a backward curve, and then, in the contact furrow, 



* " Note on a Very Fine Example of Helicoceras stevensoni, etc.," ' Bull. Am. 

 Mus. Nat. Hist.,' vol. xiv (1901), p. 219, pis. xxix and xxx. 



f Loc. cit., 1S76, p. 484, pi. xxi, fig. 3 (perhaps a fragment of a Didymoceras ?). 



j Hyatt (loc. cit., p. 577) calls Hamites fremonti, Marcou (holotype in B.M., 

 Geol. Soc. Coll., No. 12667), probably a gerontic stage of some species of 

 Exiteloceras, which is doubtful, the former probably being of Albian age, and 

 close to "Anisoceras alternatum," Pict. & Camp, non Mantell (loc. cit., 1861, 

 pi. li). Helico. pariense, White, also, in the writer's opinion, is not an Exiteloceras, 

 and with the so-called " Crioceras ellipticum, Mantell," of Schliiter and other 

 authors, and similar Turonian forms, belongs to a new, unnamed genus. 



Loc. cit. (1894), pp. 568 and 571. 



|| Loc. cit. (1880), pi. xiv, fig. 7, and loc. cit. (1901), pi. xxx. This form seems 

 to differ from the species here described only in the uncoiling of the body- 

 chamber. 



