THE NAUTILUS. 131 



In addition to the variation noted above, which is observable 

 throughout the series, certain individuals show others. Nor- 

 mally the spire is on a level with, or slightly below, the plane 

 of the whorls. Shells 1 and 4 conform to this feature fairlv 



V 



well. But in 2 and 3 the second to the last whorl is higher 

 than either those preceding or the body whorl, and in 3 its 

 plane is quite oblique. Shell g shows this in a less degree. 

 Series c and d show this variation well. 



Normally the whorls increase slowly and gradually to the be- 

 ginning of the campanulate expansion. From this nearly all 

 the specimens show various diversions, as shown in series a. 

 Shells 4 and 5 approach the type most closely. In 3 and 6 the 

 second to the last whorl is proportionately much the largest. 

 In 3, 4 and 5, the whorls are rounded above except for the last 

 volution, which is sub-carinate. In 2 and 7 the tops of the 

 whorls are quite carinate. From the umbilical aspect as shown 

 in series 6, these differences are not apparent, the whorls being 

 rounded to sub-carinate below. 



The lines of growth are coarser, though not to a large degree, 

 in some specimens than others. Shell 5 is unique in having a 

 series of revolving lines as well. These fade away as they ap- 

 proach the aperture, and are most numerous about the middle 

 of the whorl. Several individuals have also rib-like striae on 

 the campanulate portion of the body whorl, but not elsewhere. 

 Revolving lines on the shell were seen only on this one speci- 

 men of those from Blue Sea Lake. 



The aperture itself is subject to considerable variation. There 

 is a considerable difference in the degree of flare, and as one 

 would expect from the varying amounts of upturn of the last 

 whorl in the obliquity of the aperture also. Shell 6 and of 

 course 8 are extreme in this regard. In 1 the degree of obliqu- 

 ity from the vertical of the plane of the aperture is 15; in 6 it 

 is 40. 



One feature, seldom seen in Planorbis campanulatus, but which 

 is comparatively common in these specimens, is a rudimentary 

 color banding. Unfortunately, this feature has not shown well 

 in the plate. These colored areas are generally confined to the 

 lower half of the whorl and consist usually of two brown re- 



