During the course of this study, eight greenhouse ranges,t devoted exclusively to the commercial production of roses, were investigated for snail populations. The ranges were located in five counties of New York State as follows: Suffolk, four; Nassau, one; Chemung, one; Niagara, one; Monroe, one. They varied in size from a range consisting of four greenhouses to one composed of 29 greenhouses with over 1OO benches of roses in production. Specimens of at least one of three species of mollusks, Zonitoides arboreus (Say), Opeas pumilum (Pfeiffer), or Lamellaxis grdcilis (Hutton), were found in all of the ranges. A single, dead, specimen of Cionella lubrica (Muller) was the only other shelled mollusk found in any of the houses. All three snail species have been recorded as part of the greenhouse fauna of Europe (Meeuse and Hubert, 1949) but no discussion of their ecology appeared in the very extensive paper. Indeed, all of the literature on these three species contains very few ecological references. The ecological factors investigated in this study are discussed under the following headings: Soil, Temperature, Moisture, Food, Population Dynamics, and Distribution. Soil.-Commercially grown roses are planted as seedling root stocks in beds ranging from 50 to 300 feet in length and two to six feet in width with an approximate soil depth of 18 inches. A bed may be in production as long as seven years without replanting. Frequently, 'different beds within one greenhouse are planted with rosebushes of different ages. When planting takes place, the soil is steam sterilized. This process is intended to destroy nematodes and other plant pests. Undoubtedly, when properly carried out, the snails or snail eggs present are also killed. In most cases, a sterilized mulch is then spread over the soil surface or the beds may be left with a bare soil surface. The snails reported here were found in be'ds with, and those without, mulch. When mulch was present it consisted of 1) manure, 2) manure and straw, 3) corn cobs, 4) corn cobs and manure, 5) corn cobs and buckwheat hulls, or 6) buckwheat hulls alone. The primary purpose of this mulch was to hold moisture, and corn cobs which are quite effective for that purpose were found in most of the beds, either alone or in some combination. All eight ranges studied made some use of cobs while manure was used extensively only in one range and buckwheat hulls in limited quantities in one other.