HALIOTIS, HELIX. 193 
§9—4. Hauiotts. Spec. 19. 
tuberculata, (sea-ear,) shell subovate, the outside 
transversely grooved, rugged and tuberculate. 
4 or 5 inches long. 
See" o. 8 
9—4, Hevix. Spec. about 380. 
Remark. The following species of the he/ia, 
including the planorbis and dyna sections, are 
taken mostly from Say and Barnes. They are 
the most common American fresh-water and shell- 
marle species. 
Section A. Proper Helix. Spire convex ; aper- 
ture wider than lung. 
albilabris, (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 thin, 
fragile, depressed, horn-colour, pellucid ; whorls 
four, irregularly wrinkled crosswise ; aperture 
sublunated ; 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-distant, acute lines, 
separated by regular grooves; aperture lunate, 
17 
