NO. 2.] DESCRIPTION OF THE FOSSILS. 73 



type of the species described by Count Keyserling, than to our Macrocephalites 

 Kcettlitsi n. sp. 



When Newton points out that in his Amm. Ishmae Keys. var. arcticus. 

 the inner whorl "encroaches more upon the outer one" than in Macrocepha- 

 lites Ishmae Keys., this is a mistake, for in Newton's var. arcticus the 

 encroachment is the same as in the one figured by Count Keyserling and 

 in the specimen of Macrocephalites Ishma Keys, examined by me. In all 

 these pieces the encroachment is somewhat smaller than in the above described 

 species of Macrocephalites Kcettlitzi n. sp. 



The proportion of the diameter (a) to the entire height of the whorl (b) 

 and to the height of the whorl in the median-plane (c) is in b 



Macrocephalites Ishmae Keys sp 100: 53: 24. 



100: 52: 22. 



var. arcticus Newt 100: 49: 24. 



Koettlitzi n. sp 100: 50: 21. 



The slight differences in the above-mentioned proportions of the various 

 forms would be of little value, if these differences were not at the same 

 time combined with differences in sculpturing. The fact that the whorls so 

 soon become smooth, distinctly characterises Macrocephalites Koeltlitzi. 



From the character of the sculpturing, the "inflated variety" of Amm. 

 (Macrocephalites} Ismae Keys. (var. arcticus) Newton (1. c. p. 501, PI. XL. 

 fig. 2.) is not allied to Macrocephalites Ishmae Keys, at all. The above-men- 

 tioned form belongs to Macrocephalites pila Nik. 1 . 



Macrocephalites sp. 

 PI. II. fig. 11. Letterpress fig. 13. 



The fragment here delineated of a chambered whorl, belongs to the young 

 form of a Macrocephalites that still has a wide umbilicus. 



The whorl is more broad than high. The low convex flanks pass into the 

 broadly convex external side without a break. The flanks incline towards the 

 umbilicus in a steep curve. 



From the umbilicus issue strong primary ribs (upon the fragment pre- 

 served there are eight), generally maintaining a radial direction. Near the 



1 S. Nikitin, 'Der Jura der Umgegend von Elatma', part 1. Nouv. M5m. de la Soc. im- 

 p<r. des Nat. de Moscou, vol. XIV. 1881, p. 11, pi. VIII. (X) figs 45, 46. 



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