JIM sr i KI i. \. 



attach the posterior end of its body to :my object, leaving the 

 arms free to exercise their prehensile power on passing object* of 

 food. This wonderful terminal sucking organ is not round in 

 any other cephalopods. but may have been possessed by the ani- 

 mal of Ammonites, supposing it to have been related to the 

 Spirula rather than the Xnntilns. The anatomy of Sjtirtilu. 

 which is carefully worked out and illustrated in Prof. Owen's 

 memoir, shows it to belong to the dibranchiate decapod cuttle- 

 fishes, as already indicated by previous studies. Whilst Spiral n 

 possesses natatory powers superior to the Nautilus, in the action 

 of its webbed arms, additional to that of the funnel, the former 

 are so small in proportion to the size of the animal, and the lins 

 are so rudimentary as to indicate sedentary habits. Prof. Owen 

 <>b-erve> that in Sjiiru/a. as in Nautilus, "the shell serves as the 

 jnn'nf <r<n>i<ni of the retractors of the funnel and of the head 

 with its locomotive and prehensile organs. Moreover, the last 

 chamber of the shell in Spinda also receives part of the visceral 

 mas>. vix.. the hind termination of the liver, which, covered by 

 its capsule, and this again by the peritoneum or a delicate 

 apom-urosis continued from the attached shell-muscles, consti- 

 tutes the hemispheric mass that fills the chamber and forms or 

 *cnds oif the beginning of the membranous siphon. 



In another memoir, Prof. Owen shows that the dorsal portion 

 of the animal of Spirula is placed towards the outer wall of the 

 shell, which is the reverse of the relative positions of animal and 

 shell in both NfiHfilii* and Ainmuniffft. showing thai the spiral 

 urowth of the shell cone took a contrary direction, lie agree* 

 that the aptychi are developed on the *p:idix of Aimiuiniti-x. and 

 are true opercular bodies; consequently the .1 in mo/i/'/c could not 

 have lu-eii like the Spimlu, an internal shell, but must have been 

 closely related to Nautilus.* 



According to some recent investigators, there is a marked re- 

 srnil. lance between the recent S/iiriflti and the fossil A iiiiiiom'fc.*, 

 particularly in the initial whorl, and a dillercnee in the latter 

 character between A in unmili'* and \iiutilnx which indicates that 

 the Aiiun'iiiitf* should be separ.-itj-d from the tet rabranchiate and 

 united with the dibi'anchiate ce|halopods. If this should prove 



wen. on the Kelntive I ' i>it inn* to tlu-ir ( 'uii>i nn-tn > of t hi- Chain- 



bered Shells of Oeplnlopods. 'Ani. ]>,<><.. >::, 1878. 



