Nautilida. 21 



modern representative, and most, if not all, of them agreed with it Nautilus, 

 in being external. GALLERY 



Modifications of the Nautilus type of shell are not unfrequent, 

 and they have given rise to several well-marked groups or genera. ,^J e-cas© 

 Thus, in Barrandeoceras the whorls are few, flattened, and very 

 slightly embracing; in Gyroceras they are numerous, elliptical 

 or subtriangular in section, and very loosely coiled; in Diseites 

 they are also numerous, compressed, and more or less sulcated 

 on the periphery; the umbilicus is wide, and has a central per- 

 foration. In some genera, as Ephippioceras in the Carboniferous, 

 and Aturia in the Eocene and Miocene, the sutures mark the 

 chief differential characters. 



The septa in the genus Nautilus are generally simple or gently 

 flexuous, but in Aturia they have a deep narrow V-shaped lobe 



Fio. 41. — Aturia ziczac, Sby., showing the elegant curved lines wMcli 

 mark the septa of the shell. London Clay : Highgate. (Nat. size.) 



on each side. Some of the Cretaceous and Oolitic species of 

 Nautilus also have very flexuous suture-lines. 



{a) Nautiloidea. — The fossil forms belonging to this suborder 

 represented in the collection are as follows : — 



No. of Species. 



12. Trocholites, Ordovician. T.-c. 71 



13. 6^yro^^rfl5, Silurian, Devonian, Carboniferous, j w ' ' 'j toWM-or 



r, rr T\ • rr ^, Table-case 



2. Ifercoeeras, Devonian. i.-c. 71 



6. Barrandeoeeras, Ordovician to Silurian SLndDexoman. ,, 71 



10. Diseites, Carboniferous. ji 71 



3. Ephippioceras, Carboniferous. ,, 71 



14. Coelonautilus, Carboniferous. ,, 71 



5. P/^Mro»aw^/Z«*, Devonian, Carboniferous, Triassic. ,, 71 

 13, Temnocheilus, Devonian to Carboniferous and Trias. ,, 71 



9. Solenocheilus, Carboniferous. ,, 71 



107. Nautilus, Trias to Recent. T.-c. 59, W.-c. 2 & 13 



6. Aturia, Eocene to Miocene. ,, 59, ,, 2 



