Land Mollusca of North America (north of Mexico)/Preface (Volume I, Part 2)
PREFACE
The present Part contains the remaining families of Helicacea, being mainly occupied with the Polygyridae.
This is the most ubiquitous and widely-spread North American family of helices, being found in all states of the Union but four (Wyoming, Colorado, Utah and Nevada), in Canada, Alaska and in Mexico. It is also more numerous in species than any other land snail family of our area, and it comprises many shells of large size.
The other family included here, Sagdidae, is a tropical group, represented in the United States mainly by stragglers from the West Indies and Mexico.
The name of my late assistant, Edward G. Vanatta, was inadvertently omitted from those to whom acknowledgments for assistance were made in Part I. Through many years he was my right hand in the long task of assorting, determining and labelling material on which this work is based.
I am indebted also to Dr. Harald A. Rehder for the generous gift of a synopsis of his notes on the apical sculpture of Polygyridae in relation to taxonomy.
As in Part I, the photographic figures for this Part are by Miss Helen Winchester, the line drawings of anatomy and shells by the author.
July, 1940.