(i) 



Palirontolofjia Sinica 



Ser. B 



are frequently dropped off or destroyed, whether l>y 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 calotte conique, 

 is evidently formed by the animal, and for its formation a reflexed 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 



Fig. 18. Diagram to illustrate the dorsal portior/of the early camerate part of the shell of a holochoanitic 

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

 portion forming the rndosipkolining; 14, endosheath which at the stage represented by fig. 17 was the last one formed 

 enclosing the endocone, (k. fig. 17); 15, /(>, 17, endosheaths since formed, 17 representing tl.e last-formed one at this stage, 

 and enclosing the endocone of this stage; i4 to ml, intersheath spaces rilled with stereoplasm; n, and o, as in fig 17; p, </, 

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

 of rl ; ;j, of r2; </, of r3 which has not yet been formed; ; si, s2, s3, first second and third camera? the last still open in 

 front, and forming with the endocone t, a part of the Hring chamber. 



reaching the basal portion of the shell, and having the power of secreting lirne, 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 than it is now in the modern Nautibi-*. 

 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 such 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 Orthoccrcis. " * 



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

 belem,nitiforme Holm, before the commencement of the outer camera?. 



It has been frequently noted, that when the outer camera 1 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 belemnitiforme. This can be accounted 

 for by the abrupt elongation of the animal's body necessary at this stage, if the animal 



* Proceedings. Amer. Assoc. Adv. Sci. 1883 vol XXXII, p. 323. 



