28 NATURAL SCIENCE. Jan.. 



Spirilla, 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 oi Belemnoteiithis, 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 

 Belevinoteuthis. 



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 Argonanto 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 oiSepiola 

 [R. palpebrosa, Owen). In 1848 he enjoyed an opportunity of dissect- 

 ing an unique but fragmentary specimen of the animal o£ Spirilla peronii, 

 and a portion of Spirula 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 shovv.id that the shells of Nautilus 

 and ammonites are revolutely spiral, or coiled over the back of the 

 animal, not involute like the Spirula, 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 Belemnitidae, 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 

 Spirula 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 Spirula, 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 



