A REPORT ON THE FAMILY MYTILIDAE 



(Pelecypoda) 



(Plates 1-10; Text-figures 1-78) 

 BY TRON SOOT-RYEN 



PREFACE 



During the cruises of the Velero III and Velero IV from 1931 to the 

 present year, a very valuable collection of mollusks has been accumulated 

 in the Allan Hancock Foundation, the major part having been collected 

 between Los Angeles and northern Peru and the Galapagos Islands, 

 regions from which large collections are very scarce. Fortunately the 

 larger part of the samples are preserved in alcohol and can be used for 

 the study of the soft parts of the mollusks, and thus are far more useful 

 than dried specimens only. The collection in the Allan Hancock Founda- 

 tion is undoubtedly the richest and most valuable known from the regions 

 investigated, and will add considerably to our knowledge of the mol- 

 luscan fauna of the Pacific coast of America when it is properly studied. 

 It is, therefore, to be hoped that trained specialists can work up this 

 material as quickly as possible. 



The present paper deals with the family Mytilidae found along the 

 Pacific coasts of America south of Oregon, though a few specimens from 

 Oregon, of species also occurring farther south, are included in the lists 

 of the material. It has been possible to make a survey of the soft parts of 

 the species and to give drawings of the mantle and other parts easily 

 visible from the outside, and of details of hinges and muscle scars of the 

 valves. Nearly all species are also represented by photographs on the 

 accompanying plates. Four species are considered to be undescribed and 

 several changes were found to be necessary in the generic placement of 

 the species and in the general nomenclature. There might, however, still 

 be a few unrecognized species of mytilids along the Pacific coast of 

 America. I am not satisfied with the treatment of genera such as Brachi- 

 dontes, Hormomya, Crenella, and Modiolus, and I believe that new 

 material and a careful study of these groups, which is highly needed, 

 is necessary before doubtful questions can be satisfactorily settled. 



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