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 is a very distinct shell for an AmpuUaria, although it 

 appears to belong to the A. ghiesbrechtii group. In the 



