1(*)4 GUIDE TO THE FOSSIL INVERTEBRATE ANIMALS. 
Gallery 
VII. 
Table-case 
3. 
Wall-case 
2 . 
Table-cases 
4 16. 
Wall-cases 
3-6 & 9 12. 
Table-case 
4. 
present day, closer study lias disclosed many diflevcnces 
lietween the Palaeozoic shells and those of the modern 
nautilus. Even the Mesozoic shells are not really the same, 
and not until Tertiary times do shells occur that can with 
more justice be referred to Nautilus as now restricted. In 
the London Clay many of these are well preserved and show 
the internal structures ; among them N. wiperialis often 
attains great size. Afnria, of wliich specimens from Eocene, 
Oligocene, and IVlioccne rocks are shown, differs from Nautilus 
in the folding of its sutures, well seen in A. ziczac. 
Further information concerning the fossil Nautiloidea in 
the Museum is given in the first two volumes of the 
“ Catalogue of the Fossil Ceplialopoda ” issued by the Tru.stees 
in 1888-91. 
Order — AMMONOIDEA. One of the earliest straight- 
shelled forms that can without doubt be referred to this 
Order is the Devonian llactritcs (Fig. 81 Ic), in which the 
septa are still unfolded, but which has a protoconch (see 
model. Table-case 1) and its siphuncle marginal, i.e., near the 
outer shell-wall. We have abeady seen, in such a form as 
Mimoccras compress^ivi (Fig. 81 n), how the straight shell 
became coiled first in its old age, and how in more advanced 
forms the coiling began at an earlier and earlier stage of the 
life-history, until even the protoconch was affected by it. 
In many of the earlier Ammonoidea the protoconch can still 
!>e seen distinctly (Fig. f>3 a), being uncovered by later whorls. 
Fxo. 93. — Goniatites. a, Pronorites cyclolobus, aud b, Glyphioceras sphae- 
ricum, Carboniferous Limestone, England, c, Agathiccras Sitcssi, 
with shell preserved, Permo-Carboniferous, Sicily. Natural size. 
(From Foord and Crick.) 
and its globular shape is ajiparent. In others the shell soon 
became more tightly coiled (Fig. 93 h), till the protoconch is 
hidden by subsec|uent whorls (Fig. 93 c). As the shell 
