304 CLASS V. CEPHALOPODA. 
Example. 
Pl. CCXCIX. Fig. 1. 
Nautitus Pompixius, Linneus (Gmelin’s edit.), p. 3369. Rumphius, 
Mus., pl. 17. f. A. and C. Martini, Conch., vol. i. pl. 18 and 19. 
f. 164 and 165. Vignette, vol. i. p. 222. Owen, Memoir on the 
Pearly Nautilus, pl. 1 to 8. De Blainville, Anatomie de la Coquille 
du Nautile, Nouvelles Annales du Muséum, vol. ili. p. 1. pl. 1 and 2. 
f. 1 and 2. Valenciennes, Nouvelles Recherches sur le Nautile, 
Archives Muséum, p. 257. pl. 8 to 11. 
Nautilus secundus, Aristotle. 
Nautilus major, Rumphius. 
Nautilus maximus, D’ Argenville. 
Order I]. CEPHALOPODA MONOTHALAMIA. 
Testa cymbeeformis, externa, illoculosa, simpliciter involuta. 
The plan which we have here adopted for the ordinal division of the 
Cephalopods was introduced more than a hundred years since by Brey- 
nius, a naturalist of Dantzic. It is not, as before stated, in good concord- 
ance with the organization of the animals, for, according to the structure 
of the breathing apparatus, as shown by Mr. Owen, there is a much 
closer affinity between the Spirula and the Argonaut, than between the 
siphoniferous genera Spirula and Nautilus. So few of the Cephaiopods 
are conchiferous, that it is extremely difficult to introduce a natural ar- 
rangement of them in a ‘‘ System of Conchology.”’ The anatomical cha- 
racters of the Mollusca can only be strictly followed in treating of the 
entire series, both conchiferous and naked; and it only remains for us, 
therefore, to characterise the monothalamous kinds referred to this order 
as having a light, open, papyraceous, boat-shaped shell, which is external 
