637 
Prams xls 
Figs. 1 and 2. Diorugoceras (Naut.) planidorsatum, after Portlock, Geod. 
Rep. Londonderry, etc., Pl. xxxv, Fig. 1; Carboniferous. Fig. 1, side view, re- 
duced considerably. Fig. 2, section of outer whorl showing how completely the 
contact furrow is moulded to the form of the whorl. 
Figs. 3-5. Pleuronautilus superbus, after Mojsisovics, Das Gebirge um Hall- 
stadt, i, Pl. xviii, Trias. Fig. 3, reduced one-third, showing the striated nepionic 
Stage, the very large umbilical perforation, free ananepionic substage, also the - 
close-coiled stages. Figs. 4 and 5, lateral, dorsal views of the fragment of what 
is probably another species reduced one-third, showing an impressed zone as 
described and figured by Mojsisovics.* 
Figs. 6-11. Digontoceras rotundum, Oolite; Coll. Mus. Comp. Zodlogy; no 
locality. 
Figs. 6 and 7, side and front views of nepionic stage and ananeanic substage, 
natural size, showing especially the large, pear-shaped umbilical perforation and 
the amount of involution which covers only about one-half of the side. The 
outer part of Fig. 6 still has remnants of the dorsal shell of the enveloping neanic 
and ephebic whorl and parts of four septa clinging to it. Two older sutures in 
the paranepionic volution and two younger in the metanepionic volution are also 
shown and first to the third are seen in Fig. 7, which also shows the narrow ana- 
and metanepionic substages. Fig 8, the same broken down, showing the apical 
chamber and ceum enlarged in Fig. 9. Fig. 10, section of ananepionic substage 
at first septum. Fig. I1, section of metanepionic passing apicad of second septum 
and showing early beginning of impressed zone, both have the venter down- 
wards. 
Fig. 12. Cenoceras (Naut.) clausum, after Barrande and Hyatt, Syst. SiZ., 
Pl. ceeclxxxix ; D’Orb. Coll. Jardin des Plantes; Oolite; somewhat enlarged, 
shows the well-defined impressed zone in the paranepionic substage and the first 
three sutures. 
Figs. 13-15. Cenoceras (Naut.) clausum (?), St. Vigor le Grand near Bayeux, 
Bronn Coll. Mus. Comp. Zoél.; Lower Oolite. Fig. 13, somewhat eniarged, 
showing the shape of umbilical perforation and ana-, meta- and part of parane- 
pionic substages. The amount of involution is shown by the dark line. Fig. 14, 
front view of same, natural size. Fig. 15, enlarged to show shape of ananepionic 
substage at first septum, the venter down. 
Figs. 16-21. Cymatoceras (Naut.) (sp. ?), Texas. Fig. 16, side view of ne- 
pionic stage, and ananeanic substage with sutures enlarged two diameters. The 
approximation of the fourth and fifth sutures appeared in several specimens of the 
young of this species. The third and fourth sutures are too close together in this 
drawing and the spaces between the fifth, sixth, seventh and eighth, somewhat too 
wide. The spaces between these last are not so wide as that between the third 
and fourth in the original, this space being also slightly less than that between the 
second and third. Fig. 17, section of apex and ananeanic substage enlarged two 
diameters with the deep zone of contact. Figs. 18 and 19, the appearance of the 
* See p. 547, above. 
