336 LECTURE XXIII. 



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

 eject into the surrounding water, and are concealed by the obscurity 

 which they thus occasion. The branchial character of the naked 

 Order of Cephalopods is an essential condition of their muscular 

 powers. The presence of an ink-bladder, therefore, in the extinct 

 Belemnites, would have implied the internal position of the shell, 

 even if other proof had been wanting ; and, by the laws of correla- 

 tion, it implies likewise the presence of the muscular forces for rapid 

 swimming, and the concomitant conditions of the respiratory, the 

 vascular, and the nervous systems. Connecting, therefore, all these 

 considerations with the detection of the ink-bag in the shell of the Be- 

 lemnite, I could not hesitate in refering the Belemnites, and likewise 

 the Spirula, on account of the ascertained internal position of its shell, 

 to the Dibranchiate order, and I, therefore, separated these cham- 

 bered and siphoniferous shells from the Nautilus and the Ammonites 

 in the Classification of the Cephalopoda, submitted to the Zoological 

 Society in February 1836. 



But the true grounds of this separation seem not to have been 

 understood by some Palaeontologists. Professor Phillips, for example, 

 in his excellent Article on Turrilites in the part of the Penny Cyclo- 

 paedia, published in January of the present year, has observed, " The 

 relations of Turrilites, Scaphites, Baculites, and Hamites to Ammo- 

 nites is very obvious ; and, as through Goniatites, this great extinct 

 group is certainly connected to the living and extinct Nautili, 

 Mr. Owen has ventured to include them all in the Tetrabranchiate 

 Cephalopoda (^Cephalopoda), leaving Spirula and the Belemnites 

 with Sepia and the Dibranchiate types. However this may be, the 

 determination of the relative affinities among the numerous fossil 

 Cephalopods, a point of great importance, must be worked out with 

 the help of other considerations than the respiratory system." I have 

 said enough to show that many other considerations than those of the 

 respiratory system, and of equal importance with them, influenced 

 me in the determination of the natural affinities of the Belemnites. 

 Leopold Von Buch, who believed that he could trace in certain slabs 

 containing Belemnites the impressions of the Cephalopods to which 

 they belonged, concluded " that the body of the animal enveloped 

 the greater part of the shell, and exceeded its length by eight or ten 

 times." * Other considerations, taken from the shell itself, prove, 

 as has already been shown, that it was wholly internal. 



M. Duval, the latest and most accurate author on fossil Belemnites, 

 reproduces the figure which M. D'Orbigny has published, and which 

 is essentially the same as that given by Dr. Buckland in his Bridge- 

 * Oken's Isis, Bd. xxi. p. 438. 



