Nautilus. MOLLUSCA. CEPHALOPODA. 229 



N. spiralis umbilicatus geniculis sulcatis, Walker, Test. Min. ly. t. iii. 

 f. 69 N. umb. Mont. Test. Brit. 191 ; Suppt. 78. t. xviii. f. 1 — Eng- 

 lish and Scottish shores. 

 Chambers ten, rounded on the sides, but nearly even on the margin, with 

 a frosted appearance on the surface. Partitions flexuous, ending at the centre 

 in a pellucid sj^ot. The geographical range of this species is extensive. It 

 occurs on the coasts of Devon and of Zetland, and I have even detected it on 

 corallines found on the surface of the sea, about the middle of Hudson's 

 Straits, in 1821, by Captain Parry. 



10. N. crassulus. — Depressed, umbilicated, and shewin'g part 

 of the interior volution. 



N. spiralis, crassus, utrinque umbilicatus, geniculis lineatis. Walker, Test. 

 Min. t. iii. f 70 — ^N. crassulus, Mont. Test. Brit. Suppt. 79. t. xviii. 

 f. 2. — English coast, rare. 

 SheU opake brown, with numerous close-set elevated joints. Sides similar. 

 Mouth placed a little oblique, scarcely clasping the body, and furnished with 

 a syphon. — The internal structure of tliese recent species can scarcely be sa- 

 tisfactorily determined. 



EXTINCT SPECIES. 



1. N. imperialis. — " Involute, umbilicate. Aperture lunate. Septa entire, 

 concave, broadest in the middle, truncated, and slightly recurved at their 

 ends. Siphunculus nearest to the inside." — Sowcrh/s Mineral Conchology, 

 t. i. — In the London clay, Highgate. 



2. N. centralis — " Involute umbilicate. vVperture bluntl}' lunate. Septa 

 entire, concave, not recurved at their ends. Siphunculus central." — Sotvcrly^s 

 Min. Conch, t. i. left hand figure London clay. 



3. N. incsqiialis. — " Spheroidal umbilicate, aperture nearly round ; septa 

 distant in the inner whorls, and approaching near together in the outer 

 whoi'ls ; siphunculus near the inner margin of the septum." — Sower. Min. 

 Conch, t. xl. lower figures. — In Chalk Marl, Folkstone. 



4. N. undulatus.—m'-'- Gibbose; surface largely undulated, sides ratlier coni- 

 cal, edge flat ; aperture obcordate, inner whorls concealed." Siphunculus 

 near the centre — Sower. Min. Conch, t. xl. In G^-een Sand, Nutfield, Surrey. 



5. N. lineatus. — "Flatted spheroidal, umbilicate, surface obscurely striated, 

 back flat, broad, with a concave line in the interior (which appears convex 

 around the cast). Aperture rather square, deeply indented by the preceding 

 whorl, septa numerous, concave, siphunculus central." — Sou'er. Min. Conch. 

 t. xli. — Inferior Oolite, Comb-down, Bath. 



C. N. elegans — " Gibbose, umbilicate, with numerous linear, reflexed, ra- 

 diating sulci." — Siphunculus central. — Sower. Min. Conch, t. cxvi. ManteWs 

 Fossils of the South Downs, p. 112, t. xx. f. 1 In Chalk Marl, Sussex. 



7' N. Comptoni — " Lenticular, carinated ; centre covered ; surface smooth ; 

 keel obtuse ; aperture acutely triangular." Less than a line. — Sower. Min. 

 Conch, t. cxxi — In Chalk Marl, Wilts. 



8. N. simplex — " Depressed, spheroidal, umbilicate, plain ; mouth limate, 

 with the angles truncate, embracing the preceding whorl ; siphuncle nearest 

 to the inner edge of the septum." — Sower. Min. Conch, t. cxxii. In Green 

 Sand. 



0. N. truncatus.—'-'- Thick, flatted, plain, umbilicate; back flat, mouth 

 elongated, four-angled ; siphuncle (oval) nearest to the inner margin of the 

 septum." — Soiver. Min. Conch, t. cxxiii.— In Lias Limestone, Bristol. 



