COLIMACEA. MOLLUSCA. HELIX. 171 



fleeted lip, and an open umbilicus in its immature stages. It has 

 no tooth on the pillar, like H. thyroidus, and H. zaleta^ is smaller 

 than the former, and less globular than the latter. 



The economy of these animals may be briefly stated as follows. 

 They subsist upon decaying leaves and vegetable fibre, under which 

 they usually shelter themselves. In moist weather, and after showers, 

 they issue from their retreats, and crawl over the leaves or up the 

 trunks of trees, until driven back by a change of* weather. In early- 

 spring they are often seen collected in groups on the sunny side of 

 rocks. In June they deposit their eggs, to the number of thirty to 

 eighty in the light mould by the side of rocks and logs. These are 

 white, opaque, and elastic ; and in about twenty to thirty days the 

 young animal issues from them with a shell consisting of one whorl 

 and a half. In October they cease to feed, and select a place under 

 some log or stone where they may be sheltered for the winter, and 

 there they fix themselves, v/ith the mouth upwards. This they close 

 by secreting a thin, transparent membrane, and as the weather be- 

 comes cold, they grow torpid, and remain in that state until the 

 warmth of spring excites them to break down the barrier, and enter 

 upon a new campaign of duty and pleasure. 



HELIX THYRO'IDUS. 



Shell convex, yellowish horn-color ; whorls Jive, delicately 

 wrinkled; aperture rounded; lip white, widely reflected ; pillar 

 with a single white tooth ; umbilicus partial. 



FIGURE 108. 

 State Coll., No. 100. Soc. Cab., No. 1015. 



Helix thyroidus, SAY ; Mch. Encyc., (Amer. ed.,) iv. Journ Acad. J\fat. Sc. i. 123, 

 ii. 161. Amer. Conch., pi. 13, f. 2. FE'RUSSAC ; Hist, des Moll., pi. 49 A. f. 4. 

 DESHAYES; Encyc. Mith., Vers, ii. 230. LAM.; An. sans. Vert., viii. 114. 

 BINNEY ; Bost. Journ. Nat. Hist., ii. pi. 18. 



Cochlea umbilicata, LISTER ; Conch., t. 91 , f. 91. 



Cochlea terrestris Virginiana, SCHROET.; Einl. in Conch., ii. 192. 



Mesodon leucodon, RAFINESQ.UE. 



Shell rounded, convex, of a uniform yellowish-brown or russet- 

 color ; whorls about five, convex, marked with delicate and 

 parallel lines of growth; suture distinct; aperture broad, semi- 

 lunar, contracted by the lip ; lip white, widely reflected, and 



