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



As Ammonites vertumnus Leckenby is synonymous with Quenstedtoceras 

 Marice d'Orb. sp., tlie form described by Sintzow. and the one here 

 described from Franz Josef Land may both be designated as Quenstedtoceras 

 vertumnum Sintzow. 



Sintzow states in his work (written in Russian) that his Quenstedtoceras 

 vertumnum resembles the early stages of Quenstedtoceras Mologce Nikitin *. 

 I can only judge of the early stage of the latter species from a figure given 

 by Nikitin 2 . According to this figure, the whorls in Quenstedtoceras Mologce 

 Nik. are thicker and more evolute, and the ribs more curved than in Quen- 

 stedtoceras vertumnum Sintzow. A further difference may be noticed from 

 Nikitin's description 8 . According to it, Quenstedtoceras Mologce has a 

 dichotomous second lateral lobe (in Nikitin's drawing of the lobes of a larger 

 specimen, the second lateral lobe is trichotomous 4 , the second lateral lobe 

 in Quenstedtoceras vertumnum Sintzow being also trichotomous). Quenstedto- 

 ceras vertumnum Sintzow and Mologce Nik. agree in having no keel- 

 formation, even in the very earliest stages known. 



Judging from its greater involution, Quenstedtoceras vertumnum Sintzow 

 is also allied to Quenstedtoceras Rybinskianum Nik. In this respect, special 

 prominence should be given to the form 5 described by Lahusen as Cardio- 

 ceras Rybinskianum. To judge from Lahusen's figures, however, Quenstedto- 

 ceras Rybinskianum Nik. differs in its greater thickness, in the absence of 

 single ribs, and in the keel-formation in a size corresponding to that of our 

 specimen, i. e. the filling up of the interspaces between the ribs in the median 

 line of the ventral area 6 . 



1 S. Nikitin (Notes sur les depdts jurassiques des environs de Sysran et de Saratov. 

 Extract from Bull, du Com. geol. St. Petersbourg, vol. VII. p. 29) confirms this remark 

 of Sintzow's but seems to regard Quenstedtoceras vertumnum Sintzow and Leckenby 

 as identical, on which point I cannot agree with him. 



2 S. Nikitin, Allgemeine Geologische Karte von Russland. Blatt 56 (Jaroslawl, etc.) 

 Mem. du Com. geol. St. Petersbourg, vol. I. No. 2, 1884, p. 59. PI. 1. fig. 3. The 

 young form here figured does not agree in its ribbing with the inner whorl of the 

 piece figured by Nikitin, 1881 (Rybinsk, etc.), PI. 1. figs. 11, 12. 



3 S. Nikitin, 1881. Rybinsk, etc. p. 51. 



4 S. Nikitin, 1881. Rybinsk, etc. PI 1. fig. 10. 



11 J. Lahusen, 1. c. PI. N. figs. 13-16, especially 13, 14. 



' W. Weissermel (Beitrag zur Kenntniss der Gattung Quenstedticeras. Zeitschr. d. 

 DeuUeh. Geol. Ges. 1895, p. 327) here uses the very upt term "Kielstreifcn". 



