The variations and ecological distribution of the snails of the genus Io . CO ^Oa,, MEMOIRS i»^, Sectional Lsbtcay OF THE NATIONAL ACADEMY OF SCIENCES .^e^T^^rO^^ V^^^^ -^r^S^l Voliame XII gecv-cv-^- P»art II SECOND ]yj_tUM:OIR WASHINGTON1915. ISTATIOlSrAL ACADEMY OF SCIEISTCES. Volume XII. SECOND MEMOIR. THE VARIATIONS AND ECOLOGICAL DISTRIBUTION OF THE SNAILS OF THE GENUS 10. BY CHAS. C. ADAMS, NEW YORK STATE COLLEGE OF FORESTHY,SYRACUSE, NEW YORK. CONTENTS Page. I. Introduction 7 II. Habits and life history of lo 8 III. The races and forms of ib 10 IV. The geographic relations of the s
The variations and ecological distribution of the snails of the genus Io . CO ^Oa,, MEMOIRS i»^, Sectional Lsbtcay OF THE NATIONAL ACADEMY OF SCIENCES .^e^T^^rO^^ V^^^^ -^r^S^l Voliame XII gecv-cv-^- P»art II SECOND ]yj_tUM:OIR WASHINGTON1915. ISTATIOlSrAL ACADEMY OF SCIEISTCES. Volume XII. SECOND MEMOIR. THE VARIATIONS AND ECOLOGICAL DISTRIBUTION OF THE SNAILS OF THE GENUS 10. BY CHAS. C. ADAMS, NEW YORK STATE COLLEGE OF FORESTHY,SYRACUSE, NEW YORK. CONTENTS Page. I. Introduction 7 II. Habits and life history of lo 8 III. The races and forms of ib 10 IV. The geographic relations of the shells examined 14 1. Powell Kiver 15 2. Clinch Kiver 16 3. Holston River drainage system 18 4. Nolichucky, Lower French Broad, and Tennessee Rivers 21 V. Quantitative variation of Jo 27 1. Variation in shell diameter 27 2. Variation in globosity or shell index. 31 3. Variation in spinosity 33 VI. The evolution of the gross environment 40 1. Introductory 40 2. From the origin of the Appalachian land habitat to the formation of the Cretaceous Peneplain 44 3. The Tertiary Peneplain and its drainage developments 46 4. The Post-pUocene and recent cycles of drainage changes 49 5. General summary 50 VII. The geographic origin of the family 51 VIIIvariationsecolog00adam
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