Nautilus. 



MOLLUSCA. 



35 



Geology and Mineralogy Considered, I. p. 359j and II. p. 63, 

 pi. 43, figs. 3 and 4. 



Involute ; sides somewhat flattened ; inner volutions 

 entirely concealed ; aperture bluntly triangular ; siphuncle 

 placed nearest to the inside ; septa concave, greatly recurved 

 at their extremities, and with a deep indentation in the edge 

 on each side, producing a zigzag appearance ; thickness 

 about a third of its diameter. 



Found in the CMay at Highgate, in London. 



24. N. STRIATUS. — The Striated Nautilus, pi. XXIV. 

 tig. 4. 



Nautilus striatus. Sovverby, Min. Conch. II. p. 183, pi. 182. 

 Fleming, Brit. An. p. 2.30. De la Beche, Geo. Manuel, 

 p. 369- 



Discoidal, somewhat gibbose, the inner volutions few, 

 entirely concealed, and increasing rapidly ; sides covered 

 with extremely strong, elevated, numerous, irregular, concen- 

 tric striaj, and having almost the appearance of ridges ; 

 umbilicus large, but not deep, in which the edges of the inner 

 volulions are slightly indicated ; ambit compressed ; aperture 

 almost orbicular, a little flattened on the back, and equal 

 to about half the diameter of the disk ; greatest diameter 

 about eight inches. 



Found not unfrequently in the Lias at Lyme Regis, Dor- 

 setshire. 



25. N. iMPERiALis. — The Imperial Nautilus, pi. XXIV. 

 fig. 5. 



Nautilus imperialis. Sowerby, Min. Conch. I. p. 9- Fleming, 

 Brit. An. p. 229. 



Discoidal, umbilicate ; inner volutions wholly concealed ; 

 sides gibbose and smooth, but striated concentrically in the 

 young state ; aperture lunate, with blunted sides ; siphuncle 

 placed nearest in the inside ; septa entire, concave, broadest 

 in the centre, truncated and a little recurved at thrir ends ; 

 umbilicus pretty large, but not deep. 



Tiiis is a widely diflr'used species, and is found in tiie Clay 

 at Highgate, near Munster, Island of .Sheppey, Brentford, 

 Suffolk, Middlesex, Essex, Berkshire, Hampshire, Wiltshire, 

 Surrey, and Kent. 



In some specimens the outer coating is of a light, chestnut- 

 brown colour, especially in young siiells, beneath which the 

 shell is of a fine pearlaceous lustre ; it is also naered within. 



26. N. BiLOBATUs. — The Two-lobed Nautilus, pi. XXIV. 

 fig. 6. 



Navlilus bilohntus. Sowerby, Min. Conch. III. p. 89, pi- 

 249, fig. 2, 3. Fleming, Brit. An. p. 230. 



Subglobose, umbilicate ; inner volutions entirelj' con- 

 cealed ; sides smooth ; back slightly flattened ; umbilicus very 

 small, and nearly cylindrical in form ; aperture transversely 

 elongated, its width being nearly four times its length ; 

 siphuncle almost central, on each side of which the septa are 

 very concave, forming two elliptical lobes ; thickness and 

 width about equal. 



Found at Closeburn, Dumfriesshire, in the Red Limestone, 

 on the property of C. G. S. Menteith, Esq. 



27. N. iNTERMEDius. — The Intermediate Nautilus, pi. 

 XXIV. fig. 7. 



Nautilus inlermcdius. Sowerby, Min. Conch. II. p. 53, 

 pi. 125. Fleming, Brit. An. p. 230. De la Beche, Geo. 

 Manuel, p. 369. 



Globose, umbilicate ; inner volutions about half exposed, 

 and increasing rapidly ; sides somewhat depressed, concentri- 



cally striated ; ambit broad flattened ; aperture a little quad- 

 rangular; siphuncle round, placed nearest the external mar- 

 gin ; septa numerous. 



I'ound at Keynsham, in Ferruginous Limestone, and at 

 Castle Hedingham, Essex. This species is nearly allied to 

 the following, but is distinguished by not being so thick as 

 the obesus, and the septa are not so numerous. The striae 

 mentioned are not, however, discernible, except when the 

 outer coating is removed. But the circular form of the 

 siphuncle at once distinguishes it from that of the obesus, 

 which is transversely oval. 



28. N. OBESUS.— The Swollen Nautilus, pi. XXIV. 

 fig. 8. 



Nautilus obesus. Sowerby, Min. Conch. II. p. 51, pi. 124. 

 Fleming, Brit. An. p. 230. De la Beche, Geo. Manuel, 

 p. 369. 



Gibbose, umbilicate ; inner volutions entirely concealed ; 

 sides plain ; ambit broad and flat ; aperture very large, some- 

 what quadrangular, its length being two-thirds the diameter 

 of the disk ; si))liuncle oblong-ovate, transverse, and almost 

 central ; septa very numerous, but not recurved, which pro- 

 duces an open form to the umbilicus, which is pretty large, 

 but not deep ; greatest diameter thirteen inches. 



Discovered in Ferruginous Limestone at Norton-Under- 

 ham by Mr Strangeways. 



Distinguished from N. intermedius by its transversely oval 

 siphuncle, which inclines inwards, and in the umbilicus 

 exhibiting no indications of the inner volutions. 



29. N. coMPLANATUs. — The Flattened Nautilus, pi. XXIV- 



fig. 9. 



Nautilus complanatus, Sowerby, Min. Conch. III. p. 109, 

 pi. 261. Fleming, Brit. An. p. 231. De la Beche, Geo. 

 Manuel, p. 464. 



Discoidal compressed, with four or five volutions ; the 

 inner ones completely exposed ; their inner edges flattened, 

 leaving a concave surface ; half of the last volution is desti- 

 tute of septa ; sides flat and smooth ; aperture lanceolate, its 

 length being nearly equal to six times its width ; near the 

 inner angle, the edge of each septum is provided with a 

 reversed sinus ; ambit rounded. 



Discovered at Scarlet, Isle of Man, by J. S. Henslow, Esq. 

 in the Slaty Limestone. 



30. N. TUBERCULATUS. — The Tuberculated Nautilus, jil. 



XXIV. fig. 10. 



Nautilus tuberculatus. Sowerby, Min. Conch. III. p. 90, 

 pi. 249, fig. 4- Fleming, Brit. An. p, 230. 



Discoidal, thick, very largely umbilicate ; the inner volu- 

 tions almost wholly exposed ; outer volutions thick, the inner 

 ones progressively descending to a deep umbilicus, the shape 

 of a reversed cone ; at about a third of the breadth of the volu- 

 tions, is situated a series of large round tubercles, which are 

 prolonged to the inner margins by a flattened rib ; the inner 

 volutions are inserted as far as the row of tubercles ; ambit 

 rounded ; aperture transversely elongated, and a little bian- 

 gular, its width being twice its length ; septa but slightly 

 concave, with their edges a little waved. 



Found in the Red Limestone at Closeburn, Dumfriesshire, 

 by C. G. S. Menteith, Esq. 



31. N. nonsALis. — The Back-siphuncled Nautilus, pi. 



XXV. fig. 1. 



Nautilus dorsalis. Phillips, Geology of Yorkshire, II. p. 

 231, pi. 17, fig. 17, and pi. 18, figs. 1 and 2. 



