Cephalopoda. 335 



The septa of the chambered cone are perforated by a marginal 

 siphon, situated in most Belemnites on the side which is nearest the 

 before-mentioned line or groove ; but in certain species of Belem- 

 nites, characterised by the flattened form of the spathose guard, the 

 siphon is on the opposite side. These Belemnites, which at first sight 

 look like distorted or accidentally compressed specimens, are peculiar 

 to certain members of the green sand formation, called the ' older 

 Neocomian.' In some species the exterior of the guard is impressed 

 with two opposite longitudinal channels in addition to the primitive 

 and constant one. 



Specimens of Belemnites have been discovered in which the spathose 

 guard has been fractured during the lifetime of the animal ; but the 

 broken portions have been held together by the investing organised 

 integuments, and have been reunited by the disposition of new layers 

 of the fibrous structure peculiar to the guard. * 



The existence of a camerated and siphoniferous structure on this 

 complex and remarkable shell, induced most Zoologists to class it with 

 the Ammonites and other more simple chambered shells. Mr. Miller 

 having detected evidence of the internal position of the Belemnite in 

 the exterior characters of the guard, first ventured upon a conjectural 

 restoration of the entire animal f ; and as only the dibranchiate type 

 of Cephalopods was then known, he placed it in the body of a 

 Calamary (^Loligo), assigning to the terminal fins the office of clasping 

 the guard and retaining it in its proper position. 



The first evidence that bore directly upon the position of the Be- 

 lemnite in the Cephalopodic class was detected by Drs. Buckland and 

 Agassiz in specimens of Belemnite from Lyme Regis, in which the 

 fossil ink-bag and duct was preserved in the basal chamber of the 

 phragmocone. We must connect with this fortunate discovery the im- 

 portant fact, that remains of an ink-bag have never been" met with in 

 connection with any of the more simple or typical forms of chambered 

 shells: we know that the ink-bag does not exist in the recent Nautilus ; 

 and it will be shown in the following Lecture that it is present in all 

 the existing Cephalopods which possess more or less rudimental in- 

 ternal shells. I ought here, perhaps, to anticipate, or recapitulate the 

 relations of co-existence of the ink-bag with the organization of the 

 naked Cephalopods, which I pointed out, in 1832, in my description 

 of the Nautilus Pompilius. The highly organized naked Cephalopods 

 enjoy active powers of locomotion, which would be incompatible 

 with the incumbrance of a large external protecting shell ; but, to 

 compensate for the want of this defence, nature has provided them 

 with the power of secreting an inky fluid, which, when alarmed, they 



* Duval- Jouve, Memoire sur les Belemnites. 4to. 1841. pi. x. 

 f Geological Transactions, N. S. vol. ii. p. 45. pi. ix. 1823. 



