Nautilus. 



MOLLUSCA. 



33 



umbilicus; ambit very broad, witli its centre plain, flat, and 

 provided with two carince on eacli side, and aroiiiKlcd broader 

 one outside of these, with a considerable smooth space inter- 

 vening betwixt them and the edge of the umbilicus ; lip pro- 

 vided with a deep sinus. 



This species has some affinit}' to Nautilus multicarinatus, 

 but it is provided with a narrow concave space in place of 

 the keel upon each side ; 



In its general contour it somewhat resembles also Nautilus 

 biangulatus pi. 23, fig. 9 ; but in addition to the angles which 

 distinguish that shell, it is provided on each side of its broad 

 and flattened front with two minor keels. 



Found in the Black-Rock, Cork, Ireland. 



6. N. CYCLOSTOMUs. — The Circle Nautilus, pi. XXII. 

 fig. 20. 



Nautilus cyclostonms. Phillips, Geology of Yorkshire, II. 

 p. 232, pi. 22, fig. 26, pi. 17, fig. 29, and pi. 18, fig. .3. 



Shell partly spiral ; inner volutions exposed, and the outer 

 cues rapidly increasing in size, to a nearly straight line ; 

 sides crossed by fine flexous striae ; sutures outwardly con- 

 cave, and slightly retroflected on the back ; aperture almost 

 circular; siphunculus placed near the outer edge; number of 

 volutions variable. 



Found at Castleton and Holland, Queen's County, Ireland ; 

 and also at High-Green-Wood. 



7. N. PENTAGONUS. — The Pentagonal Nautilus, pi. xxii. 

 fig. 21. 



Nautilus pentagonus. Sowerby, Min. Conch. III. p. 89, 

 pi. 249, fig. 1. Fleming, Brit. An. p. 230. 



Discoidal, with five volutions ; the inner ones concealed 

 to the extent of one-third, and increasing rapidly in size ; 

 ambit subcarinated ; aperture orbicular, obscurely five angled, 

 and considerably indented by the preceding volution, and 

 extending to nearly half the diameter of the shell ; sides 

 somewhat flattened, with a few oblique, slight wrinkles ; 

 septa rather numerous, and slightly concave ; the sipliuncle 

 central. Greatest diameter eight and a-half inches. 



In the young condition, the aperture is less pentangular 

 than in the adult. 



Discovered in the Black Limestone at Bathgate, Linlith- 

 gowshire, and has since been found in the Red Limestone, at 

 Closeburn, Dumfriesshire. 



8. N. siNUATus. — The Sinuous Nautilus, pi. XXII. 

 fig. 22. 



Nautilus sinuatiis. Sowerby, Min. Conch. II. p. 213, pi. 

 194. Fleming, Brit. An. p. 231. De la Beche, Geo. 

 Manual, p. 369. 



Very thick, umbilicate ; inner volutions few, and entirely 

 concealed ; sides depressed, conical, with close, moderatelj' 

 fine, and elevated concentric striae, which gradually become 

 obsolete towards the aperture ; ambit convex ; aperture 

 obtusely sagittate and truncated ; septum greatly elevated 

 towards the front, with a large marginal sinus on each side ; 

 umbilicus very shallow ; siphunculus placed a third the 

 length of the aperture from the ambit. Greatest diameter 

 five inches ; and its thickness two and a-half inches. 



Found in the Inferior Oolite at Yeovil. 



9. N. ASTACoiDES. — The Little Lobster Nautilius, pi. 



xxin. fig. 1. 



Nautilus a.ilacoides. Phillips, Geologj' of Yorkshire, I. 

 p. 163, pi. 1-2, fig. 16. De la Beche, Geo. Manuel, p. 369. 

 Shell discoidal subumbilicate ; inner volutions entirely 



pi. XXIIL 



concealed ; ambit narrow towards the inner side next the 

 aperture, but greatly tliiekeiicd as it approaches the aperture 

 behind ; sides smooth, concentrically lineated, with transverse 

 lines of growth ; aperture very expansive, occupying nearly 

 two-thirds the diameter of the shell, and rounded towards 

 the back ; sipliuncle nearly central. 



Found in the Upper Shale of the Lias formation of York- 

 shire. 



10. N. UNDULATUS. — The Waved Nautilus, 

 fig. 2. 



Nautilus vndulalus. Sowerby, Min. Conch. I. p. 87, pi. 

 40. Fleming, Brit. An. p. 229. De la Beche, Geo. Manuel, 

 p. 293. 



Gibbous ; inner volutions concealed ; sides considerably 

 produced, with large undulations, which are more deeply 

 defined as they approach towards the back, and reaching to 

 more than half the diameter ; edge of the back, when viewed 

 in profile, deeply scalloped ; aperture somewhat obcordate ; 

 siphuncle nearly central ; septa rather numerous, each crossed 

 on the surface by an undulation ; thickness half the diameter 

 of the disk. Greatest diameter twelve inches. 



Found in the Greensand at Nutfield, Surrey. 



11. N. oxYSTOMus The Sharp-Mouthed Nautilus, pi. 



XXIIL fig. 3. 



Nautilus oxystomus. Phillips, Geology of Yorkshire, IL 

 p. 233, pi. 22, fig. 35, 36. 



Lenticular, greatly depressed ; consisting of four volu- 

 tions, the inner ones half exposed ; sides smooth ; ambit 

 acute ; septa outwardly concave, as exhibited in the figure. 



Found in Limestone, at Enniskillen and Florence Court, 

 Ireland, and in the Isle of Man. 



12. N. TRUNCATUS — The Truncated Nautilus, pi. XXIIL 

 fig. 4. 



Nautilus truncatus. Sowerby, Min. Conch. II. p. 49, pi. 

 123. Fleming, Brit. An. p. 229. De la Beche, Geo. 

 Manuel, p. 369. Lister's Conchology, No. 1048. 



Thick, inner volutions entirely concealed, umbilicate ; 

 sides flattened ; ambit flat ; aperture elongated and quad- 

 rangular, extending to nearly half the diameter of the disk, 

 narrowest towards the ambit ; siphuncle oval, placed nearest 

 the inner end of the aperture, or inner margin of the septum ; 

 septa very numerous, but not recurved towards the umbilical 

 region ; thickness not quite half the diameter. 



13. N. SIMPLEX. — The Simple Nautilus, pi. XXIIL fig. 5. 

 Nautilus simplex. Sowerby, Min. Conch. II. p. 47, pi. 



122. Fleming, Brit. An. p. 229. De la Beche, Geo. 

 Manuel, p. 293. 



Spheroidal depressed ; inner volutions entirely concealed ; 

 sides plain, umbilicate ; aperture lunate, with truncated 

 angles, which embrace the sides of the volutions ; septa 

 numerous and somewhat flattened ; siphuncle situated near 

 the inner edge of the septum ; thickness nearly four-fifths, 

 the greatest diameter of the disk, which varies from an inch 

 to thirteen inches. 



Found plentifully in the Greensand, near Boreham, in 

 the vicinity of Warminster. 



This shell bears a considerable similitude to N. impcrialis, 

 pi. 24, fig. Jj, but is more rounded in its curvature, and 

 somewhat narrower and flatter in the middle. 



14. N. ExcAVATUs. — The Excavated Nautilus, pi. XXIIL 

 fig. 6. 



Nautilus excavatus. Sowerbj', Min. Conch. VI. p. 55, pi. 



t 



