193 



CadOCeraS. Fischer. 



Group of Cadoceras modiolare, (I'Orbigny, and Elatmæ, Nikitin. 



Cadoceras crassiim. nov. sp. 



PI. IX, figs. 1,2,3, and X, flg. 1. 



Six more or less complete casts of this Ammonite have 

 been found in Vardeklöft and on some of these the shell is 

 partly preserved. The casts occurred in concretions in a very 

 micaceous clay-shale 550 — 580 metres above sea-level. 



The largest specimen has a diameter of 140""*' and its 

 dimensions and their proportions to one another are as 

 follows: — 



of about of about of about of about 



Diameter UO™"! (= 1) I24™°i (= 1) 57°"» (= 1) 



Width of umbilicus 34 >> (=0.24) 27 » (=0.22) 17 ■> (=Озо) 



Height \ of the xvhorl ^ ^^ " '^=^'^^^ ^~ " (=0-43) 25 ■■ (=0,44) 15">" 



Thickness/ \ 100 » (=0,7i) 84 « (=0,68) 40 » (=0.70) 20 » 

 Proportion of the height of 



the whorl to the thickness 0,6i 0,62 0,62 0,75 



The very involute outer whorls are broadly convex on the 

 sides, but bend down steeply and suddenly towards the umbilicus. 

 The greatest thickness of these whorls occurs at about a third 

 of their height. In cross-section they are broadly horse-shoe 

 shaped. The penultimate whorl is embraced by the outer whorl 

 to half its height. The inner whorls are higher and narrower 

 than the outer. The umbilicus of the adult shell is deep and 

 somewhat narrow. Little more than the umbilical border of the 

 inner whorls is visible. The length of the body chamber and 

 the shape of the aperture is unknown. The whorls are covered 

 with strong ribs which cross the sides either in a quite straight 

 line or in shallow, backward-bending curves. At about the 

 thickest part of the whorl, the ribs divide into two — or very 

 rarely into three — branches. No tubercles are present at the 

 points of bifurcation. The ribs usually pass straight across the 

 external area or occasionally form very slight curves which 

 are convex forwards. On the last whorl, or body-chamber, the 

 XXXI. 13 



