NAUTILUS. 11 



1. Nautilus l^evigatus, If Orb. Plate II, figs. 1 and 2. 



Nautilus l^evigatus, D'Orbigny. Paleont. rran9. Terr. Cr^t., pi. xvii. 



N. testa glohosd, Icevi, umbilico minimo aut nullo ; aperturd semi-circulari ; septis parum 

 arcuatis ; siphinculo subcentrali. 



Shell globose, smooth, with the back and sides uniformly rounded, and a very faint 

 line running along the middle of the back ; umbilicus very small and entirely concealed 

 in the inner whorls ; septa slightly arched, with nearly straight margins ; siphuncle a little 

 in front of the centre j mouth nearly semi-circular, but rather wider than high, deeply 

 indented by the preceding whorl, with a broad shallow mesial sinus. 



This shell attains a large size. A specimen from Brighton measures 4^ inches in 

 diameter and ^\ inches in breadth. 



N. IcBvigatus is one of the commonest of the cretaceous, species, and is found throughout 

 the whole range of the Chalk, viz., in the Upper Chalk near Brighton ; in the Middle Chalk 

 near Maidstone, Hemel Hempstead, and Tring ; in the Grey Chalk at Dover and Lewes ; 

 in the Chloritic Marl of Bonchurch in the Isle of Wight; and in the Chalk mth siliceous 

 grains at Chard stock and on the coast of Dorsetshire. It is found in France in the Upper 

 Green Sand, the Lower and Middle Chalk. 



The only cretaceous species of Nautilus for which this could be mistaken, are N. 

 BoucJiardianus, D'Orb. andiV. simplex, Sow. {N. Clementinus ? D'Orb.) both of which have 

 a more marked umbilicus, and a depression on the ventral margin of the septa ; the latter 

 is also a less globose shell, and has the siphuncle nearer the ventral than the dorsal margin. 



2. Nautilus expansus, Sow. Plate II, figs. 3 — 5. 



Nautilus expansus, Sowerby. Min. Conch., t. 458, fig. I. 



— Archiacianus, If Orhigny . Paleont. Franc. Terr. Cret., t. xxi. 



N. testa injlatd, later aliter compressiiisculd, umbilicatd, subtiliter striatd ; umbilico 

 sub-carinato ; aperturd lata sub-pentagond; septis iindulatis ; siphunculo sub-centrali. 



Shell globose, with sloping slightly flattened sides and a sharply defined umbilicus ; 

 surface elegantly marked by fine sharp lines of growth, which are deeply incurved in front ; 

 whorls increasing rapidly in size and nearly concealing the preceding whorls ; septa very 

 flexuous; siphuncle within the centre of the septum; mouth about as broad as high, 

 somewhat pentangular, rounded in front, with nearly straight sloping sides deeply 

 indented by the inner whorl, and with a deep, broad, rounded sinus. 



Diameter 2^ inches, breadth IJ inch. 



N. expansus is confined to the lowest bed of the Chalk ; it is rare in the Chalk Marl of 

 Hamsey near Lewes, and in the Chloritic Mai-1 of Bonchurch in the Isle of Wight ; and 



