178 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 20 



INTRODUCTION 



The purpose of this survey was to study the collection of the family 

 Arcidae from the west coast of America and the Galapagos Islands, 

 collected for the Allan Hancock Foundation during the cruises of the 

 Velero III and the Velero IV from southern California to northern 

 Peru and the Galapagos Islands. 



Twenty five species are present in the material. Descriptions of most 

 of these species will be found in Maury (1922) and in Hertlein and 

 Strong (1943). A complete review of the Mesozoic and Cenozoic 

 Arcidae from the Pacific Slope of North America, with numerous illus- 

 trations, is given by Reinhart ( 1943). A good bibliography for the family 

 is also included in his paper. The synonymies will be found fairly 

 complete in Maury (1922). Anatomical studies of five of the species 

 present have been made by Heath (1941). One or more samples of 

 nineteen of the species are preserved in alcohol. The following six 

 species are represented by dried material only: Barbatia (Calloarca) 

 alternata (Sowerby), Acar pusilla (Sowerby), Anadara tuberculosa 

 (Sowerby), A. (Larkinia) grandis (Broderip and Sowerby), A. {Sca- 

 pharca) cumingiana (Nyst), and Sheldonella delgada (Lowe). The 

 circumstances did not allow a detailed anatomical study. However, easily 

 seen characters, such as the presence of eye-spots on the mantle margin, 

 and of a byssus, have been described. Schematical drawings have been 

 made of the general appearance of the soft parts from the lateral and 

 dorsal sides, and of the abdominal sense organs. 



The systematic arrangement is, with a few changes, that of Reinhart 

 (1943). The subfamily Noetiinae is retained in the family Arcidae. 



The number of species has been too small to allow a revision of the 

 systematics of the family. For that, it will be necessary in the future 

 to make more comparisons with species from the Atlantic coast of 

 America, as well as from the western Pacific. 



