40 University of Michigan 
sharp, often somewhat expanded externally ; columellar margin 
whitish to orange in color, and reflected so as to further close 
the umbilicus; inside of aperture infuscate with chestnut, 
darker towards edge, with the bands showing through, and 
with the upper portion lighter and often whitish near the 
suture. Operculum (figs. 3 and 4) horny, thin, pear-shaped, 
dark-brown in color (smoky amber by transmitted light), and 
considerably smaller than aperture; outside concave, dull and 
marked by growth-lines externad to the submarginal nucleus, 
or even laminating into thin layers at the edges; internal mar- 
gin sigmoid with vertical, crescentic boss above the nucleus ; 
inner surface with fine, radiate, subspiral striations; muscle- 
scar dull and of same shape as operculum, not extending 
internad to nucleus; extranuclear portion with smooth, shiny 
deposit, which often obscures the radial lines. 
Shell very variable in shape; some specimens are not shoul- 
dered but globose, with the last whorl descending, so as to 
raise the spire considerably above the aperture, the latter not 
greatly expanded. Two color-forms were obtained, as indi- 
cated above. One has the ground-color light olive-green, 
shading to creamy yellow near the suture; the other has it 
chestnut-brown, shading to smoky golden near the suture. The 
first form was obtained from the shores of a rocky island in 
the main lake, the second in a small but very deep body of 
water in a subsidiary crater-cone, with the water surface about 
100 feet in diameter. This small body of water was separated 
from the main lake by a rock ridge about 60 feet high and 
300 feet wide. More variation in shape was apparent in the 
small number obtained of the first form. The type (fig. 4) 
belongs to the second form. 
This 1s a very distinct shell for an Ampullaria, although it 
appears to belong to the A. ghiesbrechtit group. In the 
