ACKNOWLEDGMENTS 



Acknowledgment is here extended to the many institutions and fiiends 

 who through their generous aid have contributed so substantially to the 

 completion of this study. The author received three grants from the Amer- 

 ican Philosophical Society, two for field work in Ecuador and Panama (No. 

 lis J, 1952; No. 154 J, 1954) and one for study at the British Museum 

 (Natural History) (No. 124, 1953), with a second visit in 1959. The author 

 is under deep obligations to the authorities of the British Museum (Natural 

 History) and especially to W. J. Rees, formerly in charge of MoUusca, and 

 the late Guy L. Wilkins for permission to examine and photograph many of 

 the types of Pacific Coast mollusks from the Cuming Collection as well as 

 facilities to study the radula slides from the unexcelled Gwatkin Collection. 

 For the 1959 visit, the author wishes to thank I. C. J. Galbraith and S. P. 

 Dance for similar privileges. Here in the United States, the author is under 

 obligations to Harald Rehder and J. P. E. Morrison for their assistance, re- 

 ceived on so many visits to the United States National Museum, as well 

 as to Wendell P. Woodring, of the United States Geological Survey, when 

 questions as to fossil determinations came up for review or discussion. The 

 author wishes to express his appreciation of the assistance received from 

 the authorities of the Academy of Natural Sciences in Philadelphia where 

 this work was first started, particularly to the late H. A. Pilsbry with whom 

 the author was so closely associated for many years and to R. Tucker 

 Abbott, now at the same institution. The author is grateful to L. G. Hertlein 

 for the loan of specimens of rare species of Pacific shells from time to time. 



On various surveys and trips along the coast of Central America and 

 South America, the author has been accompanied by many geologists and 

 engineers too numerous to mention here. In Costa Rica and Panama, the 

 author was accompanied by R. A. Terry on many arduous trips, mainly 

 for geological investigations but on which collections of both fossil and 

 marine molluscan shells were generally secured. Notably amongst these 

 expeditions in Panama were the ones to the Darien and the Pearl Islands; 

 the Los Santos Province and to the Burica Peninsula, all in 1935. During 

 parts of 1935 and 1936, the author accompanied by O. D. Boggs of the 

 International Petroleum Company travelled along the greater part of the 

 coast of western Colombia and Ecuador between Buenaventura and the 

 Gulf of Guayaquil, and except for stretches of mangrove, the traverse was 

 made largely on foot. This long trek of many months offered opportunities 

 for collecting at many remote locaHties and to assemble data on regional 

 distribution. 



Smce the beginning of this study of the Pelecypoda in 1953, two major 

 expeditions have been made to Ecuador and Panama, both aided in part 

 by grants from the American Philosophical Society. On the first of these 

 in 1953, the author was accompanied by two famed collectors and students 

 of Recent mollusks, T. G. McGinty of Boughton Beach, Florida, and J. 

 Weber of Miami. Alfred G. Fischer, at that time geologist for the Inter- 



