HELIX. 



85 



of the shell in the umbilical region and causes a distinct fold without the 

 shell. A most singular feature is revealed in the structure of the parietal 

 laminje. With an ordinary magnifying power, small swellings are seen 

 at close intervals along these laminse, which, when magnified four hundred 

 diameters are seen to be surmounted with from five to ten sharp spines 

 pointing towards the aperture. 



These swellings appear to coin- *'S- -^^ • 



cide in number and position 

 with the raised ribs without 

 the shell, though they are not 

 formed at the same time: for 

 as these laminae approach the 

 aperture they become attenu- 

 ated and disappear. The sur- 

 face upon which these laraiute 

 rest is granulated, and not 

 smooth as is generally the case 



with the interior of shells. It is difficult to imagine the use of these spiny 

 projections, unless they may act in some way as points 

 of resistance to the animal for the support of a very Fig. 153. 



heavy shell. 



Jaw long, narrow, very slightly arcuate, ends 

 pointed ; concave margin slightly notched. 



Lingual membrane with 78 rows of 13 — 1 — 13 

 teeth each ; centrals tricuspid, central cusp very long ; laterals 

 of same shape but bicuspid ; uncini short, broad, serrated. 



Parietal laminae of Hdix labyrinfhica. 



Jaw of Helix lahy- 

 rinthica. [Morse.] 



Fig. 154. 



Lingual dentition of Helix lahyrinthica. [Morse.] 



Helix ]llll>1)ardi|i Bkown. — Shell umbilicated, depressed, thin, ob- 

 liquely striated above, smooth below, reddish horn-color; whirls four and 

 a half to 5, convex, regularly increasing, the last but slightly descending ; 



