inhabiting the United States. 407 
apex outward, with their very prominent elevated 
strie of increase, give it a considerable resemblance 
on the upper surface to the Poryevnx of Say, but on 
the base the similarity ceases. The aperture in- 
cluding the teeth is very much like that of Hrix 
gularis, Say, but is smaller in proportion to the size 
of the shell, and the teeth are shorter and less lam- 
ellar, while they are equally prominent.  'The 
oblique striz, so distinct on the upper surface, cease 
entirely at an obtuse carina on the upper part of the 
outer whorl, leaving the base smooth. The base is 
rather lighter in color than the upper surface, and is 
indented in the centre. The umbilicus is nearly or 
quite obsolete. The edge of the lip is brown. The 
whole surface sometimes, and the base often, reflects 
a metallic lustre. 
The teeth within the. à pérpire are in general 
formed of a single lamina or fold, but sometimes one 
or both of them are bifid or even trifid. In some 
specimens, I have observed a second pair of teeth, 
throtigh the base of the shell, at the distance of three 
fourths of a volution ` from the aperture, with indis- 
tinct marks of a third set yet further removed. 
These internal teeth (in this and in other species) 
undoubtedly mark certain periods of increase. ‘The 
growth seems to go on actively for a time by the 
addition of new testaceous matter, indicated by the 
oblique stri», and then alternates with a’ season of 
repose, when thé teeth and aperture are formed and 
used. It is quite likely that these periods are annual. 
The teeth appear never to be entirely absorbed and 
removed, although the aperture near which they 
