28 NATURAL SCIENCE. JaN., 
Spivula, in the order Dibranchiata. The examples of Belemnites oweni 
upon which this memoir was founded, were subsequently shown by 
later investigators to belong to the animal of Belemnoteuthis, an extinct 
member of the existing squid family, and the animal of the true 
Belemnite proved to be characterised by the presence of an internal 
pen or pro-ostracum not found associated with the fossil remains of 
Belemnoteuthis. 
In the same year Professor Owen communicated to the Zoolo- 
gical section of the British Association two papers detailing the 
** Further Experiments and Observations on the Argonauto argo,” by 
Madame Jeannette Power, the originator of marine aquaria. He 
prefaced them with some remarks on the relation of the animal of the 
Paper Nautilus to its shell. The experiments which proved that the 
dorsal arms were the fabricants of the shell instead of the mantle, as 
in the Pearly Nautilus, had been suggested to Madame Power by 
Professor Owen. He has also described Rossia, a sub-genus of Sepiola 
(Ie. palpebyosa, Owen). In 1848 he enjoyed an opportunity of dissect- 
ing an unique but fragmentary specimen of the animal of Spivula peronit, 
and a portion of Sfivula reticulata, and contributed the results to the 
‘“* Zoology ” of the ‘‘ Voyage of H.M.S. ‘Samarang.’” Thirty years 
later he returned to the subject of the structure of this interesting 
genus. 
In 1878 Professor Owen discussed with much vigour ‘ The 
Relative Positions to their Constructors of the Chambered Shells of 
Cephalopods.” In this paper he showed that the shells of Nautilus 
and ammonites are revolutely spiral, or coiled over the back of the 
animal, not involute like the Sfvuwla, and maintained the opercular 
character of the aptychi, which had been doubted by Keferstein and 
Waagen. He reiterated the opinion that they correspond to the 
fibrous hood of Nautilus pompilius, and are the calcifications of an 
ammonite hood. ‘The fact that no trace of the ink-bag has ever been 
found with any fossil ammonite although that organ occurs abun- 
dantly in the fossil Belemnitide, is cited as conclusive evidence that 
the Ammonites were tetrabranchiates protected by an external shell, 
and he points out that the occurrence of the protective ink-bag in the 
Spivula proves that mollusc to belong to the more active dibranchiate 
order, with an internal chambered shell—the homologue of the 
phragmacone of the Belemnite. 
The ink-bag does not occupy the last chamber of Spivula, as had 
been maintained in Woodward’s “ Manual of the Mollusca.” The 
situation of the small pyriform ink-bag in that genus being “ rectal,” 
as Owen first demonstrated in 1848. It is denied that the septated 
condition of the many-chambered shells of the Nautilus was related 
conditionally to the generative function and periodical increase, as 
had been asserted by Professor Seeley and by Dr. Henry Woodward, 
for the reason that the formation of such chambers commences from 
the embryonal cup (‘‘ protoconch’”’) and continues through an early 
