MONOGRAPH OF THE GENUS 

 ABGONAUTA, Linnams. 



Molluscum Cephalopodum. 



Testa involute discoidea, unilocularis, papyracea, minute granu- 

 lata, alba seu pallida, disci margine nigrescente ; anfractibus bica- 

 rinatis, tuberculatis ; lateribus radiatim liratis ; spira immersa. 



The " paper sailor " is a testaceous receptacle formed by the 

 female Cephalopod for the deposition and care of her eggs. It is 

 secreted by the hinder pair of arms, which in the female are ex- 

 panded into broad membranes, and have been regarded as the 

 sails of a ship-like vessel ; but they principally serve to envelope 

 the shell after its formation. 



Description of the Species (the Shells). 

 Plates 257, 258. 



1. Argo (f. 1, 2), Lanik. — Testa subcompressa, transverse 

 oblonea, lateribus planiusculis; rugis tenuibus, numerosis; carina 

 angusta, concava, tuberculis numerosis acutis ; apertura subtri- 

 gona, angusta; marginibus prope axem profuude arcuatis, incras- 

 satis, in angulis plus minusve auriculatis. Obs. This is the most 

 compressed species, the sides gradually converging to a narrow 

 keel, with very sharp tubercles. From the large scpaare-mouthed 

 shell with the angles of the mouth produced into auricles, to the 

 transversely elongated and more finely ribbed varieties, with 

 scarcely any angle, the gradations are too minute to admit of 

 specific distinction. 



2. Grtjneri (f. 9), Bunker. — Testa prsecedenti similis, sed 

 parva, transverse valde elongata ; carina convexa, latiuscula, mi- 

 nute verrucosa. Obs. Much more elongated than A. argo ; wider 

 at that part of the aperture which is farthest from the spire. 

 The keel tubercles become more and more obtuse, till at the 

 outer edge they almost disappear. 



