640 
siphuncle at about the same age. Fig. 16, another specimen from same locality, 
showing the dorsal furrow in both metanepionic and paranepionic substages. 
Both the last are enlarged 2 diameters. 
Figs. 17-19. Aturia Morisst Michellotti; Baldasseres, Mus. Comp, Zodlogy ; 
Tertiary. Figs. 17 and 18, front and side views of the nepionic and neanic stages 
enlarged 6 diameters. Fig. 19, nepionic stage, showing the umbilical perfora- 
tion, seen from the exterior as a small black spot. 
Figs. 20-22. Aturia 2izac, Sow.; Mus. Comp. Zodlogy; Tertiary. Figs. 20 
and 21, side or front view of specimen from Dax, Bronn Coll., enlarged ten times, 
showing apical character, siphuncle, first septum with deep lobes and czecum. 
Fig, 22, side view of fragment of another specimen with umbilical perforation, 
ananepionic substage in section and siphuncle. 
PLATE XIV. 
Fig. 1. Zutrephoceras De Kayt. Reduced one-third. Two dorsal sutures, 
showing the linguee form, minute, median saddles. 
Figs. 2-5. Larrandeoceras Sternbergi (sp. Barrande); Schary Coll., Mus. 
Comp. Zoél. Reduced one-third. Fig. 2, from Lochkoy, variety in which 
whorls do not touch at all. Fig. 5, section of one, same locality, in which whorls 
barely touch, showing that it has no contact furrow. Figs. 3 and 4, specimen in 
which whorls touch in ephebic stage, but become free at the base of the living 
chamber. ‘This has throughout a flattened dorsum, but no contact furrow. The 
appearance of a furrow in Fig. 4 is due to compression. These figures show also 
the narrow dorsal lobes of the sutures. 
Figs. 6-12. Schroederoceras tubulatum, n.s. Reduced one-third. Coll. Mus. 
Comp. Zoél.; Loc., Brevig, Norway; Silurian. Figs. 6 and 7, nepionic stage. 
Figs. 8-12, ana- and metaneanic substages. 
Figs. 13 and 14. Didymoceras nebrascense (sp. Meek). Reduced one-third. 
Loc., near Buffalo Gap, So. Dakota; Coll., Yale University Museum ; Cretaceous, 
Views of the parephebic substage and gerontic stage. 
Figs. 15-17. Lmperoceras Beecheri. Reduced one-third. Loc., near Buffalo 
Gap, So. Dakota; Yale University Museum; Cretaceous. Fig. 17 shows the 
earlier stages with Hamites-like whorls from above. Fig. 16 shows the similar 
apex of Fig. 15 corresponding in age to part of Fig. 17. Fig. 15, side view of 
Fig. 16, giving the ephebic stage with its tubercles and bifurcated costa and the 
parephebic substage with single costz and no tubercles. 
Figs. 18-21. Ptychoceras crassum ; Whitfield Coll., U.S. National Museum; 
Loc., Boulder, Col.; Cretaceous. Fig. 18, side view of ephebic and gerontic 
limbs, with gerontic umbilical perforation, reduced one-third. Fig. 19, section of 
same, natural size, showing the gerontic contact furrow. Fig. 20, view of dorsum 
of gerontic limb, in and just orad of gerontic umbilical perforation, natural size ; 
shows the gerontic dorsal furrow, with dorsal crests in lines of growth and one 
costation and below the contact furrow. Fig. 21, section of the upper end of 
Fig. 20, showing the gerontic dorsal furrow. 
