No. 418.] NOTES ON LIVING NAUTILUS. 825 
same figure, 4. This difference was clear in the case of the six 
specimens I examined ; but I later found that there must be 
considerable variation, for in looking over the shells obtained 
at Manjuyod I was unable to distinguish those of the females 
from those of the males in as many instances as three out 
of ten.! 
Another character of the shell is the great number of irreg- 
ular growth lines which they often present (Fig. 5). These 
lines show frequently, as in the figure at *, an undulation of 
a somewhat regular pattern, reminding one of the markings 
Fic. 5. — Shell of Nautilus. Outline sketch showing undulatory lines of growth. 
formed at the septal rims in Ceratite or Goniatite. Doubtless 
this peculiarity in recent shells has already been commented 
upon, and the point made that the irregular growth lines can- 
not be directly related to those of the fossil forms, since they 
are not connected with the formation of septa, several being 
Sometimes found on the wall of a single chamber. They are 
interesting, however, I suggest, as representing à tendency 
uring special periods of shell-forming activity, perhaps after 
3 ‘I find that Willey gives (1895, Wat. Sci., p. 412) a similar note, stating that 
"in most adults the shell can readily be identified as belonging to male or feine, 
but often this identification is very difficult, and in young shells impossible. 
figures extremes of difference. 
