



96 POMPECKJ. JURASSIC FAUNA OF CAPE FLORA. [NORW. POL. EXP. 



QUENSTEDTOCERAS, (Hyatt. Nikitin.' 



GROUP OF QUENSTEDTOCERAS MOLOG^-RYBINSKIANUM NIK. 



The genus Quenstedtoceras in the material before me is represented by 

 a single specimen only. To judge from its sculpture, it belongs to the group 

 Quenstedtoceras Mologce-Rybinskianum so widely spread in the Upper Callo- 

 vian of Russia, and it may be identified with a species likewise described 

 from the Russian Jura, viz.: 



Quenstedtoceras vertumnum Sintz. 



(Non vertumnum Leek. Lah., etc.) 



PI. II. fig. 9. Letter-press figs. 20, 21. 



1888. Quenstedtoceras vertumnum. I. Sintzow, Carte geol. gener. de la 

 Russie. F. 92. Saratow Pensa. Mem. du Com. geol. 

 St. Petersbourg. Vol. VII. No. 1, p. 109. PI. I. fig. 5. 

 The young form figured is flat, discoid, involute, and with a rather 

 narrow umbilicus. The section of the whorls is oval, higher 

 than it is broad, diminishing towards the outside. The 

 Fig. 20. greatest thickness is at about half the height of the whorls. 



Quenstedtoceras The ventra i area j s not s harp, but bluntly rounded. At a 

 vertumnum Sintz, 



Section of the diameter of 19 mm. the specimen shows the following propor- 

 whorl of PJ. II. , ,. 



Fig. 9. Nat. Size. tlons of dimensions: 



Diameter 19 mm. 1 



Width of the umbilicus . . . 6 0.32 



Height ) ( 8 mm. 0.42 



J of the last whorl . 

 Width ) ( 1 0.34 



The moderately convex whorls are thickly covered with rather coarse 

 ribs. In the lower half of the whorls, the ribs are sharper, towards the out- 

 side, they become more rounded. They have a slightly falciform curve. 

 In the last third of the present whorl, dichotomous ribs alternate with single 

 ribs; on the preceding part of the whorl, there are more dichotomous ribs. 

 They run across the ventral area in curves, with the convexity towards 

 the front. The intervals between the ribs are not filled up on the external 

 surface, so that no keel-formation takes place. 



1 Hyatt first wrote Quenstedioceras (Proceed. Boston Soc. Nat. Hist. XVIII. p. 391); 

 this is evidently a printer's mistake. The correct spelling of the name is Qwnstedto- 

 ceras and not Qnenstedticeras, as used by most authors. 



