2 10 
Mr. Say on the genus Ocythoe. 
be remote from the shell in one part, and impressed by its 
asperities in another. 
Such also is the form of the inferior part of the abdomen, 
that it never could have revolved in the cavity of the invo- 
luted spire ; yet we have never been informed that the vacated 
spire has been either broken or solidified. Neither is there 
any attachment whatever between any part of the body and 
the including shell, by an organ appropriated to that office. 
In consequence of this organization, the ocythoe cannot adapt 
itself to the form of the cavity in which it rests, or secure 
itself there so completely as the well known parasitic paguri 
are enabled to do, in consequence of the pliability of their 
vesicular abdomen, and by the agency of their terminal hooks 
or holders. Such observations seem to afford presumptive 
evidence of the parasitic nature of these animals. 
It does not appear to me probable that the Ocythoe ascends 
to the surface of the water by exhausting its shell of the in- 
cluded water ; for if this were the fact, those females whose 
shell is in great part filled with eggs, could not visit the 
surface. But the change of specific gravity is doubtless 
effected in its own body, by which it is enabled to sustain 
itself on the surface at will, or to descend to the bottom 
promptly at the approach of danger. 
The shells which in structure and appearance approach 
nearest to argonauta, are unquestionably to be found in the 
Pteropoda; and the examination of Carinaria, Atlanta and 
Spiratella, would almost lead us to suppose, that the artificer 
of argonauta is in reality of that division ; but if this suppo- 
sition be indicated by the conformation of the shell, it does 
