THE SHELL 105 



v. The aperture of the pedal gland (p. 120) is 

 immediately below the inferior lip, between 

 the head and the foot. 



Pass a seeker into it, and backwards along the gland. 



B. After Eemoval of the Shell, 



Twist the animal out of the shell, taking care not to 

 damage the upper part of the body in so doing. The shell 

 comes off readily if the snail has been put in spirit for a short 

 time after drowning. 



I. The shell. 



a. The colour varies a good deal in different specimens. 



The ground colour is a yellowish brown, marked 

 by darker longitudinal bands running round the 

 spiral, and by transverse bands corresponding to 

 the lines of growth. 



b. The nucleus is the oldest part of the shell, at the top 



of the spiral, corresponding to the umbo of the 

 mussel-shell. 



c. The mouth is oval, and notched posteriorly by the 



penultimate turn of the shell. Its lip is smooth 

 and slightly everted. 



d. The lines of growth are transverse ridges parallel 



to the mouth of the shell, indicating successive 

 positions of -"the mouth during the growth of the 

 shell. 



e. The umbilicus is an opening on the under surface 



of the shell leading into the hollow axis or 

 columella. It is not always present. 



Clip away one half of the shell with bone-forceps, and grind 

 tlie cut edges flat on a file or stone. 



f. The columella is the axial portion of the shell round 



which it is coiled ; it is formed really by the inner 

 wall of the several turns, each of which overlaps 

 rather more than half of the preceding one. 



