NATJTILID^. 
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curved on the sides of the shell, but they form a conspicuous sinus 
on the periphery. The body-chamber is unknown. 
This species most nearly resembles Nautilus elegans^ J. Sow., hut 
it differs therefrom in respect to its general form, which is more 
quadrate, viewed in section ; moreover, the siphuncle is nearer the 
inner (dorsal) margin than in N. elegans, and the ribs are straighter 
on the sides of the shell and more frequently subdivided than they 
are in the last-named species. 
Horizon. Gres Yert (Upper Greensand). 
Locality. Honfleur (Calvados), France. 
Represented in the Collection by a single example. 
Nautilus semiundatus, Foord. 
Sp. Char. Shell (cast) inflated, especially in the young shell, 
very slightly compressed on the sides, broadly rounded on the peri- 
phery. Umbilicus closed ; margin rounded. Greatest width of the 
Nautilus semiundatus.—a, lateral view of a cast (No. 88590 h), showing nearly 
the whole of the bofly-chamber with the constriction near the margin of 
the aperture ; h, peripheral view of another specimen (No. 37901), showing 
the coarse ribbing, limited to the peripheral area. The dark lines crossing 
the figure represent the sutures. Both figures are drawn from specimens 
in the British Museum ; a is about one seventh, h a little over one fourth 
natural size. 
shell in the umbilical region. Septa somewhat distant, being Ij 
nches apart in the median line of the periphery, near the body- 
