628 
PLATE VII. 
Figs. 1-3. Schroederoceras tubulatum, Hyatt, pars Lit. angulatus, Saem.; 
Coll. Mus. Comp. Zoél., Loc., Brevig, Norway. Reduced one-third. Fig. 1, side 
view of the fragment; the free whorl is restored as shown in this figure. The 
suture and form of the restoration was taken from the well-preserved dorsum and 
cast of the interior of the right side of the free whorl. The umbilical perfora- 
tion is probably incorrect. The aperture follows the lines of growth, but is very 
likely incorrect and the ventro-dorsal diameter may be too long. Fig. 2, section, 
the outer volution being restored as regards the venter and right side; the dorsum 
and left side are accurate. Fig. 3, restored outline of living chamber at termina- 
tion showing the obliteration of the impressed zone. See also Figs. 6-12, Pl. xiv. 
Figs. 4-6. Schroederoceras casinense, Quebec Group; Loc., Fort Cassin; U. S. 
Nat. Museum, Coll. Walcott. Natural size. Fig. 4, side view showing living 
chamber aperture. Fig. 5, dorsum of living chamber with aperture and ephebic: 
volution. This shows contact zone in the ephebic stage and its disappearance 
upon the free volution; the whorl was broken away and removed at xx. Fig. 6 
showing dorsal crest of the aperture and replacement of impressed zone by a gib- 
bous surface just beyond the shaded area in Fig. 5. See also PI. vi. 
Figs. 7 and 8. Schroederoceras Eatoni (sp. Whitf.), Hyatt, Quebec Group ; 
Loc., Fort Cassin; U. S. N. Mus,, Coll. Walcott. Natural size. Fig. 7, side view 
showing lines of growth, sutures, and aperture. Fig. 8, front of same with ventral 
sutures and rim of aperture removed showing the remnants of impressed zone. 
See also Pl. vi. 
Figs. 9-12, Lstonioceras perforatum, Schréder, Silurian. Fig. 9, side view 
after Schréder, Pal. Abh. Dames et Kayser, v, Pl. xxvi, Fig. 1 a, reduced one- 
third, showing free nepionic and free gerontic volutions with lines of growth. 
Figs. 10 and 11, Loc., Reval, Mus. Comp. Zoél., Bronn Coll., showing parane- 
pionic whorl with lines of growth on the dorsum and absence of dorsal furrow 
and lateral sutures, reduced one-third. Fig. 12, three sutures of upper part of 
dorsum of the paranepionic substage of Figs. 10 and 11, the shell removed and 
the. whorl enlarged. 
Figs. 13-19. Estontoceras biangulatum, Silurian ; Loc., Breslau; Mus. Comp. 
Zool., Kranz Coll. Figs. 13 and 14, reduced one-third the abdomen of Fig. 13, is 
distorted by pressure.* Fig. 15, venter of paranepionic and section of neanic 
below with beginning of impressed zone (this is more accurately given in Fig. 
15 a); above is ephebic whorl, but this and sutures are distorted by perspective. 
This view is taken from the interior of Fig, 13 with parts between fractures re- 
moved. Fig. 16, venter of ephebic stage, showing sutures with ventral lobes not 
saddles as on outer volution of Fig. 15. Fig. 17, dorsum of free gerontic volution 
showing lines of growth with dorsal crests, sutures with dorsal lobes ; depression in 
cast perhaps annular muscle, which disappears on the sides; there are faint marks 
on the venter as if the upper edge of this may have risen intoa saddle on that side 
as in Fig. 1, Pl. viii, of Remeléceras. The impressed zone disappears early on this 
volution. Fig. 18, venter of the same, showing change in sutures and return of 
*The apex of this was not clearly seen and it may be free. 
