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



doreras Tchefkini d'Orb. sp. PI. II. fig. 3b shows (much enlarged) the 

 sculpture of the innermost whorls; single ribs do not appear until later - 

 see the second half of the last whorl on PI. II. fig. 3a, fig. 2, 1 and letter- 

 press fig. 16 a. 



Occasionally it is to be observed, that a primary rib, issuing from the 

 umbilicus, is replaced at about half the height of the whorls by two secondary 

 ribs rising from the outside, and passing behind and before the primary rib 

 letterpress fig. 16 a, at the place marked by the arrow. 



In larger sizes than those with a 30 mm. diameter, the ribs gradually 

 become coarser, and the intervals wider; the ribs run almost straight across 

 the flanks, with a considerable forward inclination. 



Besides the impression of a small specimen, there is a fragment of a 

 large individual, embedded in a fragment of gray, very finely-grained, and 

 sandy hard marl (partly impression) which on account of this simultaneous 

 occurrence must be regarded as an old specimen belonging to the young 

 forms just described. In its sculpturing, this specimen agrees perfectly with 

 that described by Newton -- 1. c. PI. XXXIX. fig. 10 - - as Amm. (Cado- 

 ceras) modiolaris Luid., "flattened variety". Both specimens show that 

 Cadoceras Nanseni n. sp. is subject in old age, to the same broadening of 

 the whorls as most of the Cadoceras (Exception: Cad. galdrinum, patruum). 

 The umbilical margin in this size is broad and obtusely rounded. On the 

 wall of the umbilicus, the primary ribs still go rather close to the umbilical 

 seam; on the flanks the ribs are mostly bifurcated; single ribs or trifurcate 

 ribs are of less frequent occurrence. On the umbilical margin, the ribs are 

 rather sharp but not swollen or coarsely tubercular. 



The lobe-line could only be observed in young specimens. It is charac- 

 terised by narrow lateral and auxiliary saddles. The siphonal lobe is nearly 



as deep as the tripartite, first lateral lobe. The second 

 lateral lobe is small and short, scarcely extending so 

 far down as the inner branch of the first lateral lobe. 

 Cadoceras Nanseni n. sp. There are two narrow, short, auxiliary lobes and also 



f'n ' '?' i a little denticle near the umbilical seam. The ends 

 at a height of the -whorl 



of 7 mm. 2 X enlarged. o f the two lateral lobes and of the auxiliary lobes lie 

 in a line inclining slightly towards the umbilicus. The external saddle is 

 high, broad and obliquely tripartite. The first lateral saddle is unsymme- 



