2 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 23 



a photograph of the holotype of Pecten squarrosus Carpenter. Dr. S. 

 Stillman Berry, of Redlands, California, presented the author with a 

 type-lot specimen of Pecten (Leptopecten) enter pes Berry. Mr. John 

 Q. Burch, of Los Angeles, at whose suggestion the author first began 

 studying the family Pectinidae, was, as he has always been, generous 

 with material, information and advice. Dr. Howard R. Hill, of the Los 

 Angeles County Museum, gave the author access to the Museum collec- 

 tion and had him identify material. Mr. Emory P. Chace, of the San 

 Diego Museum of Natural History, contributed valuable ecological data. 

 The assistance given by each of the above is deeply appreciated. 



The author is especially grateful to two friends: Dr. Leo G. Hert- 

 lein, of the California Academy of Sciences, San Francisco, and Prof. 

 F. K. North, formerly with the University of Vancouver and now 

 living in San Mateo, California. Dr. Hertlein, who has studied the 

 Pectinidae for many years, and contributed greatly to our knowledge 

 of the family, supplied reference data, discussed many taxonomic prob- 

 lems, and made many helpful suggestions. Prof. North's generic re- 

 vision. The Fossil and Recent Pectinidae, Their Origin, Development, 

 Distribution and Classification, to date unpublished, is a superb and 

 most comprehensive work, and was a major influence on certain of the 

 conclusions reached regarding generic problems. 



The plate figures, unless otherwise credited, are the work of Mr, 

 Merwin Slawson, Santa Maria, California. 



Captain Allan Hancock's interest in marine research and generosity 

 in providing the means for its furtherance have enormously benefited 

 that branch of the natural sciences, and the author adds his acknowledge- 

 ment of gratitude to those previously expressed by many other workers. 



INTRODUCTION 



The Pectinidae are a large and heterogeneous family of marine 

 pelecypod mollusks, world-wide in distribution, having a known geologi- 

 cal history dating from the Triassic period, and recorded living at a 

 maximum depth of 2463 fathoms. 



As in other molluscan families, a great many taxonomic problems 

 exist, problems which can be satisfactorily solved only by the correlated 

 efforts of geologists, malacologists and conchologists. A monographical 

 treatise on the Pectinidae is needed, of course, but the size and diversity 

 of the family are such that even a work dealing with only the living 

 species would take many years to complete. The more practical alterna- 

 tives are either generic monographs or papers on the fauna of various 

 regions. 



