(T) 60 



Pa Jfco n toJ or/in Sinica 



Ser. B 



are frequently dropped off or destroj^ed, Avhether by accident or design, remains 

 undetermined. The truncated end of the shell is then covered over by a new deposit of 

 calcareous material of distinctive form and design. This "apical cap " or calolte conique, 

 is evidently formed l)y the animal, and for its formation a re flexed shell-secreting portion 

 of the body is necessary. Barrande supposed that the animal possessed long palmate 

 brachial appendages more or less analogous to those of Argonauta. These were capable of 



Fijf. IS. Diagram to illustrate the dorsal portion of tJie early camerate part of the shell of a holochoanitic 

 naiitiloid cephalopod. (See fig. 17). ./, " old " shell or shell of " siphuncle ". j' , j\ continuation of same into camerate 

 portion forming the I'mhixi/iholiiiin;/; U, endoslieatli which at the stage represented by fig. 17 was the last one formed 

 enclosing the eiidoconc, (/;. fig. 17); 15, 16, /7, endosheaths since formed, /? repri'^eiiting tie last-formed one at this stage, 

 and enclosing the endocone of this stage; mi to m" , intersheath spaces filled with stereoplasm; », and o, as in fig 17; p, ij, 

 inner shell-lining of caiiicnr, forming the sejital necks or funnels; rl, r2, septa of camerate portion; (o. forms septal neck 

 of rl ; J), of r2; tj, of )3 which has not yet been formed) ; si, s2, «3, first second and third camera? the last still open in 

 front, and forming with the endocone t, a part of the lirinfi chnmher. 



reaching the basal portion of the shell, and having the power of secreting lime, they 

 repaired the broken apex, reproducing the characters of the shell. Hyatt, on the other 

 hand, considered that this outer shell-secreting organ was homologous with the fold of the 

 mantle in Nautilus "This" he says, "is an active shell-secreting organ, which was 

 certainly present, and also functionally active, in the Ammonites and Nautiloids, and 

 probably more important in these ancient forms tlian it is now in the modern Xaut'dus. 

 This is also more consistent with the structure of the Belemnoid, which, as is easily seen 

 in the famous example of the preserved animal, had no si;ch pair of enlarged arms and 

 yet deposited exteriorly, a solid covering, the guard, which is in our opinion the 

 homologue of the solid filling of the truncated end of Orthoccras.'" * 



A similar organically deposited layer of lime covers the initial end of Vaginoccms 

 belemnitiforme Holm, before the commencement of the outer camera?. 



It has been frequently noted, that when the outer camera? begin building, the 

 diameter of the inner shell or " siphuncle " is more or less abruptly contracted. This is 

 found in Cameroceras in Nanno and in Vaginoceras belemnififorme. This can be accounted 

 for by the abrupt elongation of the animal's l)0(ly necessary at this stage, if the animal 



* Prori'ediiigs. Amer. Assoc. Adv. Sci. ISS::! vol XXXII, p. 323. 



