ARGONAUTA. 133 



Family III. ARGONAUTID^E. 

 Genus ARGONAUTA, Linn. 



The shells of Argonauta, although numerous species have been 

 described, are all referable to three groups, and may not exceed 

 that number of distinct species. These types are : 



1. That of A. hians. Ribs few and distant, keel broad. 



Here belong, besides the type, A. Conradi Parkinson, 

 cornuta Conrad, dispar Conrad, gondola Dillw., Owenii 

 Adams, polita Conrad and Kochiana Dunker. 



2. That of A. Argo. Ribs numerous, closer ; keel narrow. 



To the type species may be added A. Gruneri Dunker, 

 compressa Bl., expansa Dall., Nouryi Lorois, Pacifica 

 Dall., fragilis Parkinson and papyria Conr. 



3. That of A. nodosa. Ribs numerous, luberculated, keel 



rather narrow. 



Within each of these groups species have been formed upon 

 the presence or absence of lateral " auricular" extensions or 

 horns of the edge of the aperture, but large suites of specimens 

 show that this character is b}' no means constant, and that it 

 exists indeed, in all stages of development. Dr. K. you Martens* 

 who was the first to perceive this grouping and the non-specific 

 character of the horns, has proposed to designate under each 

 species four forms, viz. : 



a. Forma mutica. Aperture narrow, lateral edges straight. 



b. Forma obtusangula. Ends of aperture margin forming an 



angle with the plane of volution. 



c. Forma aurita. Ends of aperture margin produced into a 



spine at right angles to the plane of volution. 



d. Forma agglutinaus. Margin of aperture angulated at its 



ends, but the angles appressed to the spire. 

 The animal of the Argonaut-shell, supposed at first to be 

 parasitic in it, has received the generic name of Ocythoe given 

 by Leach as from Rafmesque. The Ocythoe of the latter author, 

 however, was not intended by him to apply to the animal of the 

 Argonauta. At any rate the Ocythoe of Leach becomes a 



* Ann. Mag. N. Hist., xx, 3d ser., 1867. 



