164 GUIDE TO THE FOSSIL INVERTEBRATE ANIMALS. 



Gallery 

 VII. 



Table-ease 

 3. 



Wall-case 

 2. 



present day, closer study has disclosed many differences 

 between 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 yjreserved and show 

 the internal structures ; among them N. imperialis often 

 attains great size. Ahiria, of which specimens from Eocene, 

 Oligocene, and Miocene rocks are shown, differs from Naittikis 

 in the folding of its sutures, well seen in ^. ziczac. 



Further information concerning the fossil Nautiloidea in 

 the Museum is given in the first two volumes of the 

 " Catalogue of the Fossil Cephalopoda " issued by the Trustees 

 in 1888-91. 



Order — AMMONOIDEA. One of the earliest straight- 

 Table-eases shelled forms that can without doubt be referred to this 

 W^l cases ^^"^^^ Devonian Badrites (Fig. 81 h), in which the 



3-6 & 9-12. 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 already seen, in such a form as 

 Mimoceras compressum (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 

 be seen distinctly (Fig. 93 a), being uncovered by later whorls. 



Table-case 

 4. 



Fig. 93. — Goniatites. a, Pronorites cyclolobiis, and 6, Glyphioceras sphae- 

 ricum, Carboniferous Limestone, England, c, Agathiceras Suessi, 



with shell preserved, Permo-Carboniferous, Sicily. 

 (From Foord and Crick.) 



Natural size. 



and its globular shape is apparent. In others the shell soon 

 became more tightly coiled (Fig. 93 h), till the protoconch is 

 hidden by subsequent whorls (Fig. 93 c). As the shell 



