7 
Wty, 
Fic. 15.—Nautilus wmbilicatus. 
V. DESCRIPTIONS. 
In treating of the history of the impressed zone it has become 
essential to describe a number of new genera and also new species. 
The old names—Gyoceras, Lituites, Nautilus, etc.—convey en- 
tirely false ideas of affinity and would serve to confuse the student 
of these fossils, since the new names ignore these groups. Thus it 
is not at all in contradiction of the nomenclature if I state that the 
close-coiled Zarphyceras prematurum of the earlier Quebec faunas 
is the last of its phylum and has no descendants in the Upper 
Silurian or later; but if I call it Nautilus, and say that Vautilus 
