830 ('LAS* XIII. 



Rossia OWEN. 



Loligopsis LAM., Perothis ESCHSCHOLTZ, RATHKE. 



LAMARCK has described this genus as having only eight arms ; the long 

 tentacula are often torn off. In common with Cranchia this genus has no 

 membranous valve in the funnel. These animals are nearly transparent ; 

 the eight arms are short ; the body is conical, posteriorly narrow and with 

 two round fins at the extremity. Compare RATHKE Perothis ein neues 

 Genus der Cephalopoden, Mem. presentes a I'Acad. imper. des Sc. de St Peters- 

 burg, n. 1835, pp. 149176. 



Cranchia LEACH. 



Sp. Cranchia scabra LEACH in TUCKET'S Exped, to the River Zaire, p. 410. 

 The fins are situated quite at the end of the body and the dorsal surface of 

 the mantle is grown fast to the head. 



Family XIV. Octocera s. Octopoda. Arms eight, large, often 

 very long, surrounding the mouth in a circular row. Body sacci- 

 form, without fins. Funnel without valve. 



Argonauta L. Arms furnished with a double row of acetabula 

 (suckers), the two superior expanded into a membrane towards the 

 extremity. Shell thin, involute, external, unilocular, with spire 

 bicarinate. 



This remarkable shelled animal excited long ago the admiration of the 

 ancients ; see PLINIUS Hist. Nat. ix. cap. 29. It was supposed that it made 

 use of its fin-shaped arms as a sail, and thus in still weather could swim on 

 the surface of the sea; but the observations of RANG (GUEEIN Magazin 

 de Zool. I837 1 ) have not confirmed this opinion; these arms lie expanded 

 along the outside of the shell and serve to fasten the animal in its shell, 

 which is not attached to it by any muscles. Many naturalists (RAFINESQUE, 

 LEACH and others) thought, that this animal like the hermit-crab (Pagurus) 

 lived parasitically in a borrowed shell, and that the shell of Argonauta 

 belonged to some unknown species of mollusc. Accordingly this genus of 

 Octopoda was named as a new genus Ocythoe. Although this animal can 

 readily move from its shell, just like some Pteropoda, this opinion is now, 

 however, sufficiently refuted. For the discrepant form of the male indivi- 

 duals which have no shell see above, p. 820 823. 



On the anatomy of Argonauta compare POLI Test. utr. Sicil. Tom. in. 

 and VAN BENEDEN Nouv. Mem. de I'Academie royale des Sc. de Bruxelles, 

 Tom. XT. 1833. 



1 POLI adopts this notion of the ancients, and he has even figured the animal in 

 accordance with it (Testae, utr. Sicil. III. Tab. 40), but says that he has never himself 

 seen the sails of the Argonauta. 



