AIIGONAUTA. MOLLUSC A. 17 



O. moschatus, Lam. Body elliptical, smooth; arms very long and 

 slender; cups in a single row. Mediterranean., &c. Lam. vii. 658v 



O. octopodia, Grant. Body rounded, smooth ; mantle connected with 

 the head behind ; suckers sessile, in a single row. Inhabits Frith 

 of Forth. Flemings Brit. An. 254. 



Division. II. CEPHALOPODA MO^OTHALAMA. * 

 Shell unilocular, entirely external, and enveloping the animal. 



This division contains only one genus. 



Gen. 5. ARGONAUT A, Lam.-r-Lin. 



Shell univalve, unilocular, involute, subscaphoid, very thin ; 

 the spire with a double keel, tuberculous, involved in the 

 aperture. 



A. Argo, Lam. Shell involute, fragile, white ; the sides transversely 

 and closely ribbed ; the keels approximate and tuberculated ; the 

 tubercles small and very numerous. Inhabits Mediterranean sea. 

 -r Klein, Osl. pi. 1. fig. 3. 



The shell of this species is commonly known by the name of the Paper Nautilus. 

 It is about 8 inches in diameter, extremely thin and fragile, and of a white colour, 

 excepting the posterior part of the spire, which is brown. It somewhat resembles a 

 little ship or galley, of the most elegant form. The animal possesses the faculty 

 of erecting an* ovate membrane at the extremity of the tentacula in the manner 

 of a sail ; and the species are often seen gliding on the surface of the water in 

 this manner when the weather is calm. When alarmed the sail is withdrawn, and 

 they sink to the bottom. It is in reference to this species that Pope has these lines ; 



Learn from the little Nautilus to sail, ' 



Spread the light oar, and catch the driving gale, v 



A. tuberculosa, Lam. Shell involute, thin, white ; the sides covered 

 with transverse rugae, tuberculated in their whole length ; keels 

 separated, the tubercles conical and widely set ; aperture with 

 two auricles at the base. D'Argenv. pi. 5, fig. C. 



A. nitida, Lam. Shell thin, glossy, yellowish, with tracts verse, obtuse, 

 and smooth rugae ; keels widely separated, their tubercles large 

 and distant. Inhabits the Indian seas. D'Argenv. pi. 5. fig. B. 



Division III. CEPHALOPODA POLYTHALAMA. 



Shell multilocular, partly or entirely internal, and inserted in 

 the posterior part of the body. 



The greater portion of the shells of this division are fossil, and many of them 

 very minute. Regarding the animals of the multilocular shells, little is known ; 

 but from AIM. Peron and Lesueur having ascertained the 'nature of the animal of 

 the sptrula, it is conjectured that the shell is either covered partially or wholly by 

 the body. The fossil remains of the shells of this division are numerous, and widely 

 distributed. For^a description of the species found in Britain see Dr Fleming's 

 History of British Animals. 



This division contains seven families, viz. 1. Shell multilocular; the septa sinuous 

 at the edges : AMMONACEA. 2. Shell multilocular ; the septa simple at the edges : 

 NAUTILACEA, RADIOLACEA, SPHERULACEA, CRISTACEA, LITUOLACEA. OR- 

 THOCERATA. 



VOL. II. B 



