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is essential, however, to call attention to the statement made else- 

 where, that the dorsal furrow begins in Nautilus umbilicatus, 

 pompilius and macromphalus in the metanepionic or at any rate be- 

 fore the gyroceran bend begins. 



The ornamentation is similar to that of the young of most other 

 genera of the Mesozoic during the nepionic stage, but the young 

 of Nautilus do not repeat the broad costae of the epinepionic stages 

 of Cymatoceras. The shell of Nautilus pompilius becomes smooth 

 in the ananeanic substage which begins when contact occurs. 



The color of the ana- and metanepionic substages are pearly, 

 the outer layer of shell being thin and colorless in Ihese substages. 

 A uniform brown spreads over the exterior in the paranepionic 

 substage. This tends to break up into transverse bands in the ana- 

 neanic at the same time that the ornaments begin to disappear. 



This breaking up into bands is due to a decided fading out of 

 the coloration which may sometimes seriously affect the stripes 

 themselves. In the metaneanic, sometimes after the coloration has 

 for a brief space been reduced, the bright, broad, brown stripes of 

 the adult appear upon a white ground. 



The form of the outline of the whorl changes in the ananeanic, 

 the sides and venter becoming flattened and being less involute, 

 the whorl repeats approximately the ephebic whorl of Nautilus um- 

 bilicatus. To speak more accurately, it would at this time be iden- 

 tical with any species that might have an ephebic form exactly 

 intermediate between Nautilus innbilicatus and pompilius, since the 

 involution of the latter is at all stages somewhat greater than that 

 of the former species at the same age. In the paranepionic the animal 

 begins to deposit calcareous matter along the lines of involution in 

 the umbilical zones and thus spreads more towards the centre and 

 increases the involution. This process really begins with the meta- 

 neanic and is often marked by a permanent constriction beyond which 

 the transverse lines of growth become coarser than they are in the 

 ananeanic substage. 



In the anephebic substage, the closing of the umbilici by the 

 spreading inwards of the calcarous deposits of the umbilical zones 

 begins and is carried out fully in the metephebic substage, the 

 umbilici being completely covered up and obliterated. In the 

 parephebic substage the brown coloration disappears, leaving the 

 surface white. No degenerative modifications other than this loss 



