MENCLATURE OF STAGES OF GROWTH WI> DECLE 9 



relations with the indubitable ha occurring upon the apices of the 



concha of Ammonoids and Belemnoida The wrinkled lump above referred to is 

 unquestionably a pari of the Bhell. It is nol only closely attached, bul the longi- 

 tudinal strisa of ih«- apex of the true conch are continuous upon the proximate 

 of the lump. It had an aperture which must have remained open until the 

 liger had entirely left the interior of the protoconch, and was 

 then closed by 1 1 1 1 - apical plate. There is o cicatrix upon tin- apex of the conch, 

 which i-< invariably concealed by the lump when it is present, and in some 

 examples we observed the fracture of the outer layer of the shell on the apex 

 of the conch and outside of the ordinary boundary of the cicatrix, which could 

 only have hot in caused by the violent removal of the lump. The wrinkled and 

 the lump when preserved can be accounted for by assuming 

 it to ! composed of concbiolin. This also accounts for its almost invari- 



able abaen ich an organ must have been easily h>-t or destroyed. The 



lumps must consequentij be regarded as the remnants of conchiolinous pro- 

 chs having elongated and narrow apertures; but probably they were, 

 when in a living condition, much larger and more oval, and more similar to the 



ouch of the Ammonoids. The continuity of the stria? from th nch to 



the protoconch also Bhows that th inch was built out from the aperture of the 



protoconch, layer after layer, and the concentric markings, and form of the apex, 

 which correlates with that of the Bear, sustain this idea. The figures on the fol- 

 lowing • less perfect than several other examples Btudied by the author 

 these were drawn. The} do not -how the passage of the external longitu- 

 dinal stii:r from the apex of the conch on t<> the surface ■•! the protoconch. 



A living chamber among recent and fossil Nautiloida marked n period of 

 iwth. The septum, therefore, was not built until the 

 animal arrived near the final Bteps, or had altogether Btopped building < >m the 

 of that part of the shell in which ii lived. At any rale, we can Bay with- 

 ir thai the septum was the final step, or one of the final Bteps, in 

 i living chamber, 

 first living chamber, or the firal larva] or naepionii Vmti- 



ented by the apex oi the conch in that order; but the 

 ptum an<! sipho in ili'l not exist at th which is represented 



it or slightly curved widely spreading cone, — in fact, the empty apex 

 of th ■ conch. The length of the first li\ ing chamber has not been ascertained ; bul 

 that it was short seems probable from the form of the cone in Nautilus. Doubt- 

 apply to the ■ in- of closelj coiled shells, in 

 which the cone was much slender* r than in existing Nautilus, and the first living 



menu, \* compared « I 



I 



