46 EOCENE MOLLUSCA. 



No. 8. Nautilus regalis. Soioerby. Tab. IV. 



Nautilus regalis. J. Sow. 1823. Min. Con. vol. iv, p. 77, pi. 355. 



— — Def. 1825. Diet, des Sc. Nat. vol. xxxiv, p. 300. 



— — Weth. 1836. Philos. Mag. and Journ. vol. ix, p. 465. 



— — Morris. 1843. Cat. Brit. Foss. p. 183. 



— — Pictet. 1845. Traite element, de Paleont. vol. ii, p. 338. 



— — Sow. 1849. Dixon's Geol. Hist. &c. p. 120. 



N. Testa laevigata, sub-ventricosd, in aspectu ventrali compressd, obscure undulatd ; 

 aperturd obtuse-ellipticd ; umbilicis obtectis ; septis simplicibus, concavis, titroque latere 

 per/mr urn undulatis, siphone sub-centrali perforatis ; lobis dorsalibus brevibus, rotundatis, 

 haud rejlexis. 



The present species is distinguishable from the preceding by the closed umbilicus, 

 and by its general form, which is less ventricose than that of N. centralis. It is a 

 smooth shell, flattened on the sides, and bluntly rounded, and obscurely undulated 

 on the ventral aspect. The aperture presents a subquadrate appearance. The 

 umbilicus is closed by a thickening of the lip, assuming the appearance of a solid 

 axis to the shell. The septa are nearly simple, presenting on each side slight undu- 

 lations, and the short, rounded dorsal lobes are deeply concave, and not reflected. In 

 the young shell the septum is characterised by a conical depression placed on the 

 dorsal margin close to the preceding whorl ; as the shell enlarges this gradually 

 decreases in size and depth, and ultimately disappears. It was of course moulded on 

 a corresponding protuberance on the animal, probably an enlargement of the epithelial 

 cincture. In some species the cavity is very deep. It was on this character that 

 De Montfort, mistaking the depression for the mouth of a second siphuncle, founded 

 his genus Bisiphites. The siphuncle is small and excentric. The lines of growth, 

 like those of the preceding species, are decussated, and reflected backwards in broad 

 undulations. 



The Nautilus regalis attained a large size. The specimen figured, for the use of 

 which I am indebted to Mr. Dixon, measures 9'5 in. in diameter, by 5 in. across. The 

 species occurs at Islington, Regent's Park, Chalk Farm, Hyde Park, and at Bognor. 

 It appears to have been one of the most common of the English Eocene Nautili. The 

 septum is represented at Tab. VIII, fig. 5. 



No. 9. Nautilus urbanus. Sowerby. Tab. Ill, fig. 2 a — b. 



Nautilus urbanus. J. D. C. Sowerhy. 1843. Min. Con. vol. vii, p. 36, pi. 628. 



— — Morris. 1843. Cat. Brit. Foss. p. 183. 



— — Pictet. 1845. Trait6 element, de Paleont. vol. ii, p. 33S. 



N. Testa discoided, in aspectu ventrali rotundatd, et obscure undulatd ; umbilicatd ; 

 aperturd subquadratd, elonyatd ; septis oblonyis, concavis, in utroque latere -Jen iter undulatis 

 et sip/ione excentrico perforatis ; lobis dorsalibus perbrevibus, oblique truncatis, haud rejlexis. 



