561 
is essential, however, to call attention to the statement made else- 
where, that the dorsal furrow begins in Wautelus 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 cost of the epinepionic stages 
of Cymatoceras. The shell of Mawtilus 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 these 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 Mawét¢lus 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 Wauwtilus umbilicatus and pompilius, since the 
involution of the latter is at all stages somewhat greater than that 
of the former species at the same age. Inthe 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 bya 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 
PROC. AMER. PHILOS. SOC. XXXII. 143.38. PRINTED JULY 24, 1894. 
