126 PROCEEDINGS OF THE MALACOLOGICAL SOCIETT. 



Order TETRABRANCHIATA. 

 Family NAUTILID^. 



Genus NAUTILUS, Linnccus. 



Type. — Nautilus pompiUus, Linnsous, Systema Naturaj, 1767, 

 ed. 12, vol. i. pt. 2, p. 1161. 



Shell smooth, pearly, discoidal, camerated ; septa concave 

 anteriorly, perforated subcentrally for passage of siphuncle, which 

 extends from the floor of the last chamber to the nucleus, and is 

 protected by a sheatli containing calcareous spicules ^ ; sutures plain, 

 curved ; last or body chamber much larger than preceding ones, and 

 bearing saddle-shaped impressions of muscles where the body of the 

 animal adhered to its shell. 



NATJTrLTJS CENTRALIS, J. Sowcrby. 



Nautilus centralis, J. Sby. — Mineral Conchology, 1812, vol. i. p. 11, 

 pi. i. left-hand figure. J. de C. Sby. — Mineral Con- 

 chology, 1843, vol vii. p. 36, pi. Dcxxvii. fig. 6. F. E. 

 Edwards. — Mon. Pal. Soc. 1849, p. 45, pi. iii. figs, la-lc, 

 pi. viii. fig. 2. J. de C. Sbv.— Dixon's "Sussex," 1850, 

 pp. 110, 121, 228, pi. xiv.'fig. 28. Foord.— Cat. Foss. 

 Ceph. British Museum, 1891, pt. II. p. 316. R. B. 

 Newton.— Syst. List Edwards Coll. British Museum, 

 1891, p. 290. 

 Characterized by the central position of its siphuncle ; shell very 

 ventricose, much rounded on the ventral aspect ; septa concave 

 outwardly and simple ; dorsal lobes broad. The specimen in the 

 Edwards Collection alluded to by Mr. A. H. Foord, and said to have 

 been found at Bracklesham (which we very much doubt), is so crushed 

 and mutilated as to be unrecognisable. 



Formation. — London Clay. Localities. — Sheppey, Hampstead 

 Tunnel, Whetstone, near Chalk Farm, Bognor, Hyde Park, Hadley, 

 Maida Hill, Primrose Hill. 



Nautilus imperialis, J. Sowerby. 



Nautilus imperialis, J. Sby. — Mineral Conchology, 1812, vol. i. p. 9, 

 pi. i. (upper and right-hand figures). J. de Sby. — Mineral 

 Conchology, 1843, vol. vii. p. 35, pi. Dcxxvii. fig. 4. 

 Edw.— Mon. Pal. Soc. 1849, p. 47, pL v. pi. viii. fig. 1. 

 J. de C. Sby.— Dixon's " Sussex," 1850, pp. 109, 120, 228. 

 Foord.— Cat. Foss. Ceph. British Museum, 1891, pt. 2, 

 p. 321. E. B. Newton.— Syst. List Edwards Coll. British 

 Museum, 1891, p. 290. 



' For details concerning these spicules see paper by H. Brooks, " Preliminary 

 remarks on the structure of the syphon and t'unuel of Nautilus pompiUus.''^ Proc. 

 Boston Soc. Nat. Hist. vol. xxiii. (1888), p. 380, pi. i. Also ante, p. 3. 



