HALIOTIS, HELIX. 193 



9 4. HALIOTIS. Spec. 19. 

 tuberculata, (sea-ear,) shell suhovate, the outside 

 transversely grooved, rugged and tuberculate. 

 4 or 5 inches long. 

 See MS. P. 



9 4. HELIX. Spec, about 380. 

 Remark. The following species of the helix, 

 including the planorbis and lymnasa sections, are 

 taken mostly from Say and Barnes. They are 

 the most common American fresh-water and shell* 

 inarle species. 



Section A, Proper Helix. Spire convex ; aper- 

 ture wider than lung, 



fdbilabris, (common snail, white-lip snail,) shell 

 thin, fragile, convex, not perforated ; whorls 6, 

 obtusely wrinkled crosswise, spirally striate, 

 with very fine lines ; aperture lunate and regu- 

 larly curved ; lip flat, white. About an inch 

 broad. 



thyroiduS) (small white-lip snail,) lip not flat^ 

 white :, a strong oblique tooth on the pillar-lip. 

 Breadth about three-fourths of an inch. 



arboreus, (dwarf snail, bark snail,) shell very thitu 

 fragile, depressed, horn-colour, pellucid; whorls 

 four, irregularly wrinkled crosswise ; aperture 

 sublimated ; lip thin ; umbilicus large and deep. 

 Breadth not the fourth of an inch. Often under 

 decaying bark of trees. 



tridentata, (three-toothed snail,) shell depressed, 



brownish or horn-colour ; whorls five, crossed 



by numerous raised, equi-distaut, acute lineg f 



separated by regular grooves ; aperture lunate, 



17 



