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Plate X. 



Figs. 1-14. Coloceras {Naut.} globatuiti (sp. De Koninck), Hyatt; Loc, Vise, 

 Belgium, Carboniferous; Coll. De Koninck, Mus. Comp. Zoology. 



Fig. 1. Side view of nepionic and neanic volution, natural size. Fig. 2, same 

 enlarged in front view and ends of volutions restored ; compare neanic volution 

 with the gerontic volution of Vestinautilus pinguis, PL ix, Fig. 17; it will be 

 seen that this genus resembles the latter in the lateral fluted faces, but has rounded 

 sides, such as have been described as appearing in the paragerontic substage of 

 that species ; Fig. 2 also shows the impressed zone well-developed in the parane- 

 pionic substage. Figs 3-6, sections of meta- and paranepionic substage of Fig. 

 10, showing development of outline and correlation of impressed zone with 

 nephritic form. The ananeanic substage begins immediately after this on the 

 latter half of the still uncoiled first volution and then the longitudinal ridges dis- 

 appear on the abdomen and also the crease or hollow central ventral zone, the 

 section becomes in the metaneanic similar to that of the upper volution in Fig. 2. 

 Fig. 7, enlarged oblique view of apex of same, showing the ana- and metanepionic 

 substages and the beginning of the impressed zone in a shaded crescent near the 

 base of the figure. Fig. 8, view of venter of another specimen ananepionic and 

 apaitof metanepionic showing the beginning of the hyponomic sinus in the 

 bands of growth. Fig. 9, end view of same with cicatrix. Figs. 10-12, views of 

 another specimen showing the first three sutures, impressed zone and ventral 

 hollow zone of the paranepionic substage. Fig. 13, shows the impressed zone 

 of the ananeanic substage and the beginning of the true impressed zone after con- 

 tact in the shaded crescent-like depression from which the apex has been removed. 

 Fig. 14, another specimen of same age with the pseudo-impressed zone and the 

 apex (ananepionic substage) in place. In all sections the venter is the lower side. 



Figs. 15-22. Pvtoceras dubium. Fig. 15, side view slightly enlarged showing 

 shape of umbilical perforation and abrupt bending of the paranepionic substage 

 when the zone begins. Fig. 16, front view of ana-, meta- and paranepionic sub- 

 stages and neanic volution in part. Figs. 17 and 18, enlarged views of same 

 without the neanic volution. Fig. 19, enlarged view of details of bands of growth 

 and longitudinal ridges taken from same. Figs. 20 and 21, views of ephelic vol- 

 ution, natural size. The history of the impressed zone is parallel with that 

 of Coloceras except that it comes in only after the abrupt bending of the first 

 whorl, and the form and character of the ana- and metanepionic substages 

 differ. Fig. 22, view of the ananepionic substage showing the flattened aspect of 

 apex. Figs. 22 and 9 (the latter described above) are, however, more distinct 

 than the specimens. 



Figs. 23-26. Ephippioceras {A^aut.) ferratum (sp. Owen), Hyatt; Loc, Ed- 

 mondson Co., Ky., Carboniferous; Mus. Comp Zoology. Enlarged four diameters. 

 Fig. 23, side of fragment of paranepionic substage, showing also umbilical per- 

 foration, apex restored and fragment of cast of ananeanic substage with parts of 

 two sutures. Fig. 26, venter of same. The longitudinal ridges are wider apart 

 and broader at their crests on the sides than on the central parts of the venter as 

 shown in Fig. 23. Figs. 24 and 25 show sections of both ends of the fragment 

 covered by shell in Fig. 23. 



