458 



MICHIGAN SURVEY, 1905. 



Of these, only the first are terrestrial in their habits and are represented 

 in Michigan by a single family, the Auriculidce, and that only by one genus, 

 Carychium. 



VII. 



MEASUREMENT AND DESCRIPTIVE TERMS. 



The length or height of a shell is the distance from the apex to the basal 

 edge of the lip, measured along a line drawn through the axis. 



The greater diameter is the greatest width, including the lip, measured 

 on a line drawn at right angles to the axis. 



The lesser diameter is measured on the same plane, but on a line at right 

 angles to the greater diameter. 



Shells are dextral or sinistral, accordingly as the aperture is on the right 

 or left of the axis, when held, apex uppermost, with the aperture facing the 

 observer. 



The remainder of the terms in common use are sufficiently indicated on 

 the following diagram: 



Fig. 1. 



a to b. 



height. 



c to d. 



greater diameter 



ap. 



apex. 



u. 



umbilicus. 



s. 



suture. 



1. 



lip. 



sp. 



spira. 



t. 



parietal tooth. 



In using the keys, it is to be borne in mind that they are framed on typi- 

 cal, mature specimens. Varietal and abnormal, or aberrant forms and im- 

 mature specimens must be determined by careful study of the descriptions 

 and comparisons with normal, adult examples. The name in parentheses 

 after the name under a figure indicates the author from whom the figure 

 is copied, not the authority for the specific name. Figures not so desig- 

 nated are original. All figures of entire shells are life-size unless otherwise 

 indicated. 



