294 CLASS V. CEPHALOPODA. ORDER I. POLYTHALAMIA. 
Pl. CCXCVII. Fig. 16. 
Noposaria WesBIANA, Nobis. 
Marginulina Webbiana, D’Orbigny, Mollusques des Nes Canaries, Fora- 
miniféres, pl. 1. f. 7 to 11. 
Family 2. SIPHONOIDEA. 
Testa loculis regularibus, siphunculo continuo percurrente. 
The family of the Siphonoidea, ‘‘ Les Siphonoides” of De Haan, ‘‘ Les 
Siphoniferes”” of D’Orbigny, includes two genera of multilocular Cepha- 
lopods, which have been associated together on account of the presence 
of a continuous siphon running from chamber to chamber through the 
entire convolution of the shell. In one genus, Spirula, it passes down 
the ventral side of the shell, but in the other, Nautilus, it perforates the 
centre. The immediate purpose of this siphon has not yet been satis- 
factorily determined ; we think, however, that in the former it may be 
intended for some hydrostatic purpose, in the latter it may be destined 
solely for the passage of the membrane which sustains the animal in its 
shell during their rotatory operation of growth. 
We are now fully acquainted with the organization and habits of the 
Nautilus, but our information is extremely limited with regard to the Spi- 
rula; the description which has been handed down to us rests indeed 
upon the testimony of a single individual, and it is only on account of 
this obscurity in its history that we retain what might otherwise have 
been considered a very unscientific mode of arrangement; for in one 
genus the shell is said to be internal, whilst in the other it is external. 
The following are the genera alluded to : 
SPIRULA. NaAuvtTILus. 
