No. 89.] 



125 



NOTE REFERRED TO 0^ PAGE 101. 



Since the preceding pages were printed, I have again compared the figure of the 

 Goniatites rotatorius of De Koninck with the species from Indiana; and not- 

 withstanding the deference I have for the European authorities who pronounce the 

 two identical, I still feel that there is room for doubt. The direction of the septa in 

 the figure of De Koninck differs from that of ours; the arch of the lateral saddle 

 in the latter is nearly central, while in the former it is near the umbilicus. The 

 form and proportions of the section of a volution differ; for while in the European 

 specimen the greatest diameter is near the middle, or nearly in a line with the back 

 of the embraced volution, the greatest diameter in ours is much within this line, 

 and near the ventral side of the volution. The depression formed by the dorso- 

 lateral lobe is nearer to the back of the embraced volution in our species, than is 

 shown in the figure of De Koninck; while the summit of the dorsal saddle is 

 longer than in our species. The figure cited is represented with an umbilicus, which 

 ours does not show; while the profile view shows a rotundity of the volutions, and 

 a depression towards the centre, not seen in the American specimens. 



On comparing the dorsal view given by De Koninck, with our specimens, we 

 find the dorsal lobe in the latter proportionally longer and more constricted above; 

 while its retral extremity is suddenly constricted, and then continued in a narrow 

 acute point. 



In consideration of these differences in the European and American forms, I 

 think it proper to propose a distinct name for the Rockford species. • 



GONIATITES IXION. 



Goniatites rotatorius of authors; G. rotatorius? page lOl of this Keport. 

 Shell depressed orbicular : volutions entirely embracing; the greatest width of 

 the volutions near the ventral side, gradually curving or flattened on the sides, 

 the back rounded; width on the back, from the points of the dorso-lateral lobes, 

 a little more than half the greatest width of the vMution. Septa as in figure 15, 

 page 101. The dorsal side shown in the accompanying diagram. 



1 2 3 



A 



Goniatites rotatorius. 



Fig. 1 & 2. These diagrams show the extremes of variation in the distance of the septa, 



form of lobe, etc. on the dorsal side of Goniatites ixion. 

 Fig. 3. Dorsal side of Goniatites rotatorius, after Dk Koninck. 



