20 
NovEMBER 9TH, 
ORDINARY MEETING.—MR J. ROBERTSON ON 
SEPIOLA OCEANICA, PLACUNA PLACENTA, 
AND DENTALIUM ENTALIS. NOTE ON THOMAS 
GEERAN. 
It was not his intention in these Notes on Shells to trouble them 
with general descriptions of the specimens submitted to them, but 
only to mention facts not generally known. 
The Sepiola before them was called atlantica by D’Orbigny, but 
further knowledge proved it to be oceanic. The body was short and 
purselike, and supported by a band; there was also a ridge which 
fitted a groove in the funnel. Until recently, the reproductive pro- 
cesses of the cuttle-fishes were involved in great obscurity. The males 
of Octopus and eledone were rare, and only females of some species 
were known. No male argonaut, but hundreds of females 
had been found. Madame Power, who kept argonauts in floating 
cages, described the newly-hatched argonaut as looking like a little 
worm, having rows of suckers with a thread-like appendage at one 
end, and a small swelling at the other. ‘‘It might be supposed to 
represent an extremely small bronchial appendage, from which the 
other parts were subsequently developed.” Madame Power, whom 
he knew in Paris, and who was largely endowed with the genius of 
observation, said that the worm-like creature was the young argonaut, 
Chiage, who seemed to be the first discoverer of this creature, 
described it as a parasitic worm. Dr. Albert Kolliker had suggested 
that these seemingly parasitic worms which had been called hecto- 
cotyles, might be the missing males. Kolliker found a hectocotyle 
adhering to the gill-chamber of a nemoctopus. Which, then, were 
they: the newly-hatched argonaut or the missing males? The per- 
manently rudimentary condition of males prevailed among parasitic 
crustaceans, the males of which lived parasitically upon the females, 
from whom they differed in form and structure. 
He would next direct attention to the Window shell Placuna 
placenta, which with P. sella (resembling a saddle), formed a group 
between ostrea and anomia, but nearer to anomia. These shells were 
nacreous and quite transparent, and had been long used in India as 
panes for windows. The shells had been known in Europe since the 
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