FAMILY 2. SIPHONOIDEA. 295 
SPIRULA, Lamarck. 
Testa ut plurimum interna, alba, subpellucida, tubulosa, in spiram dis- 
coideam, anfractibus disjunctis, convoluta; septis transversis, intis 
convexis, regulariter divisa; siphunculo continuo, propé ad ventra- 
lem partem percurrente ; aperturé integr4, marginibus simplici- 
bus, acutis. 
The interesting little discoid shell which Lamarck distinguished with 
the generic title of Spirula, was described by Lister, Linnzus and others, 
on account of its multilocular construction, as a species of Nautilus ; by 
those however, who, like D’Argenville and Martini, did not observe a 
binominous formula of nomenclature, it was introduced under the com- 
mon appellation of the Cornu Ammonis. All naturalists seem to have 
agreed upon its immediate relation to the Nautilus, and when the soft 
parts of this mollusk were discovered by Péron and Lesueur, their con- 
clusions were singularly confirmed ; for it was found to be a decapodous 
cephalopod, inhabiting the deeper waters of the ocean. But however 
strikingly these mollusks may resemble each other in their habits and 
general organism, they differ materially in regard to the office and position 
of their shell. In the Nautilus it is external and protective, the soft parts 
being lodged within the porch or aperture of the shell; but in the Spirula 
the shell is internal. The body of this cephalopod is not unlike that of 
the cuttle-fish ; the sack-like mantle is divided at the lower extremity 
into two equal lobes, and the shell lies concealed between them, having its 
attachment strengthened by the accession of a tendinous filament pene- 
trating the siphon. 
The discovery of the Spirula in a living state was hailed with especial 
enthusiasm by many, because it was reckoned to assist the ingenious 
supposition that the Foraminifera might be the analogical appendages of 
animals of similar organization ; the cephalopodic nature of these bodies, 
however, still remains to be determined. The natural history of the 
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