ANIMALS. 219 



chamber the largest, and containing the animal : siphon central, or marginal and 

 internal." (Owen.^j 



This is the only known Permian Tetrabranchiate family. 



Genus Nautilus, Linnaeus. 



Diacjiiosis. — " Shell discoid, spiral, multilocular, with simple walls. Whorls con- 

 tiguous, the last whorl enveloping the others. Chambers numerous, formed by 

 transverse partitions, which are concave towards the side facing the aperture : they 

 are perforated by a tube, and their edges are simple."^ (Lamarck.) 



This is the longest-lived genus of testaceous Cephalopods. It has existed from 

 the earliest organic age to the present time, — seeming to be scarce in species 

 during one period, and numerous in another : at present, it is represented only by the 

 three species, Nautilus Fompilius, N. umhilicatus and N. virgatus, — which are confined 

 to the Southern Ocean.^ 



Nautilus Freieslebeni, Geinitz. Plate XVII, figs. 13, 14, 15, 16, 20, 



(?) Ammonites,* Sedgwick. Trans. Geol. Soc. Lond., 2d series, vol. iii, p. 118, 1829. 

 (?) — „ Proceedings of the Geological Society, vol. i, p. 204. 



NAtTiLUs ,, Phillips, Lardner's Cyclop., Geology, vol. i, p. 190, 1837. 



— Freieslebeni, Geinitz. Neues Jahrbuch, p. 637, pi. xi, fig. 1, 1841. 



— — „ Gsea von Sachsen, p. 95, 1843. 



— — „ De Verneuil, Bull. Soc. Geol. de France, 2""° serie, 



vol. i, p. 36, 1844. 

 (?) Ammonites (?) Sedgwick. Op. cit. 



— „ Geol. Russ., vol. i, p. 226, 1845. 



Nautilus Freieslebeni, Geinitz. Op. cit. 



— — „ King, Catalogue, p. 14, 1848. 



— — „ Howse, Trans. T. N. F. C, vol. i, p. 237, 1848. 



— — „ Versteinerungen, p. 6, pi. iii, fig. 7 a, b, c, 1848. 



Diagnosis. Whorls slightly increasing in size ; with a broad flatly-rounded back ; 

 marked with delicate incremental striae. Sejjta slightly sinuated at the sides. 

 Aperture somewh-at squared, having the greatest diameter from side to side. Siphonal 

 sheath situated in the inner third of the septa.^ 



^ Cyclopsedia of Anatomy, loc. cit. 



~ Animaux sans Vertebres. The following is the diagnosis published by Linnaeus: "Testa univalvis, 

 isthmus perforata concamerata, polythalamia." 



3 For a description of the animal of Nautilus, see Professor Owen's 'Memoir on the Pearly Nautilus;' 

 ' Lectures on Comparative Anatomy,' vol. i ; and the article 'Cephalopoda,' in the 'Cyclopaedia of Anatomy,' 

 vol. i. 



* Vide Appendix. 



'•> " Die Starke der Windungen nimmt nicht bedeutend zu, der Rucken ist breit gerundet, die Kammer- 

 acheidewande bilden an den Seiten einen sehr schwachen Sinus. Die Miindung ist etwas hoher als ein an 



