84 POMPECKJ. JURASSIC FAUNA OF CAPE FLORA, [norw. pol. exp. 



convexity, broad exterior side, and flat flanks with a marked downward 

 flexure with Nikitin's ^ drawing of a Cadoceras Tchefkini. It is a frag- 

 ment corresponding to half the width of the whorl. On both the interior 

 and the exterior sides very faint, flat, broad lines, curving sharply forwards, 

 are visible as the remains of the sculpture, which becomes very indistinct 

 in large specimens 2. On the outside of the fragment, at its anterior extre- 

 mity, part of a broad, moderately deep contraction, with a distinct for- 

 ward flexure has been preserved. Cadoceras Tchefkini, like Cadoceras 

 Elatmae Nikitin and also like Cad. subloeve Sow. sp.^, bears a contraction 

 behind the edge of the mouth. 



Among the specimens from Elmwood described and figured by Newton 

 as Ammonites (Cadoceras) Tchefkini? d'Orb., the exceedingly involute form 

 with very narrow umbihcus * figured 1. c. PI. XXXIX. fig. 5, is no doubt 

 identical with our specimen ^. 



S. Nikitin, 1881, Rybinsk, etc. pi. III. fig. 21. 



Judging from a large specimen from Rybinsk determined by Nikitin in the Munich 

 Museum, Cadoceras Tchefkini does not become quite smooth, as one might think from 

 the drawings of d'Orbigny and Nikitin ; but at a more advanced age the ribs loose 

 their distinctness and tiirn into very faint, flat lines. The decrease in distinctness 

 seems to commence at very different periods in different specimens. 

 According to a large specimen from Wiltshire (Munich Museum). 



In the anterior part of the last whorl, the umbilicus of the above-mentioned specimen 

 suddenly widens, probably through crushing of the piece. — Newton's measurement 

 of the width of the umbilicus — 1. c. p. 496 — only agrees as far as the last fifth 

 of the last whorl is concerned. Where the umbilicus is entire, its width agrees with 

 that generally met \vith in Cadoceras Tchefkini. 



Newton's Amin. {Cad.) Tchefkini'^ d'Orb. 1. c. pi. XXXIX. fig. 4, agrees in proportions 

 and sculpturing (entire ribs appear to be absent) with Cadoceras stenolohum (Keyserl.) 

 Nikitin. Ainni. (Cad-) modiolaris Newton, PI. XXXIX. fig. 9. represents a full-grown 

 specimen of this species. The proportions agree in every respect with C. stenolobum 

 Nikitin (Der Jura der Umgegend von Elatmae. 1. PL V. fig. 29), and the sculpturing 

 too agrees with this species. Newton refers in his fig. 9 to C. modiolare Nikitin from 

 the Lower Callovian of Elatma (Nikitin, I. c. 2, pi. XL fig. 48). In this species as 

 well as in C. modiolare Luid. of the English authors {= C, subloeve Sow. sp. and 

 modiolare d'Orb. sp), the radial ridges on the umbilical margin, and farther in the 

 primary ribs on the umbilical wall, are distinctly visible. Newton's specimen cannot 

 be made to agree with any of these "modiolaris" species, as the umbilical margins 

 and walls appear smooth until far back. The great width of the umbilicus prevents 

 Ihe reconciling of the piece in question with C. Tchefkini; it can therefore only be 

 regarded as C. stenolobum. 



