57 



minute ; membranes of the anterior arms rounded or suborbicular, 

 extending half way to the base of the arms ; periphery occupied 

 by the attenuated portion of the arm, which near its extremity 

 passes upon the disk of the membrane, and terminates abruptly 

 near the base of the expansion ; the membrane is carinately de- 

 cun-ent on the inferior surfoce of the arm near the base of which 

 it terminates ; the inferior surface of the membrane is brassy, and 

 more numerously maculated than the superior, which is pale. 

 Length from the disk to the tip of the abdomen 2 inches. 

 Length of the abdomen 1? " 



Greatest breadth of abdomen 1 '|io " 



Length of the alated arms / 2| " 



Length of those of the opposite side 5 " 



Eggs subovate, attached to a delicate pedicle by a small basilar 

 tubercle. These fill the involuted spire in the specimen, besides a 

 considerable portion of the body of the shell. 



The suckers are very like those of 0. CrancJm, but the arms 

 are much more elongated, and the abdomen longitudinal with 

 respect to the head. This animal seems not to be unfrequently 

 the prey of some of the larger fishes, for in addition to the in- 

 stance above mentioned, Bose informs us that in his passage between 

 Europe and America, he found a specimen in the stomach of a 

 Cm-phsena equiselis, Grmel., but very much decomposed j and in 

 the musevma of Mr. Peale, in this city, a fine Argonauta occurs, 

 which was taked from the stomach of a shark. 



With respect to the contested question relative to the parasitic 

 nature of the animals of this genus, I believe the remark will hold 

 good generally, if not absolutely, that those molluscous animals 

 that form the shell in which they reside, are more or less connected 

 with it by muscular or membranaceous attachment, or by the per- 

 manent spiral form of the posterior part of the body ; and that the 

 body of the animal complies with the inequalities of the chamber 

 of the shell, or rather that the shell is moulded upon the body, so 

 as to be in contact with it in every part. So careful are they to 

 fill the cavity to its very summit, that when from their increase of 

 growth, the apex of the shell is vacated in consequence of its 

 straightness, either that part is removed by the animal, and ad- 

 ditional calcareoas matter is secreted to close the aperture thus 

 formed, or it is permitted to remain and the cavity is filled up by 



7 



