188 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 109 



8, and pi. 25, fig. 5). The differences in tooth characteristics seem to 

 be more constant. 



Another specimen that Dall placed under M. intermedia is shown in 

 plate 19, figure 7. In shape it is similar to M. arenaria but the pallial 

 sinus and hinge are more like those of M. truncata. This shell is no 

 doubt a Mya pseudoarenaria, which apparently never attains the 

 large size reached by M. japonica. Dr. Rehder, who kindly checked 

 for me the specimens in the U. S. National Museum labeled M. 

 intermedia, found that none of the large specimens has a pallial 

 sinus like that shown (pi. 19, fig. 7). It becomes obvious that Dall 

 placed two different species under M. intermedia. 



Although I have not seen the type of M. pseudoarenaria, nor any 

 specimens identified as belonging to this species, it is almost certain 

 that the shells from Point Barrow belong to it. The fossil specimens 

 pictured by Schlesch do not show the pallial sinus clearly but he 

 considers his species synonymous with M. truncata forma ovata 

 Jensen, and specimens of the latter from Greenland, lent me by Dr. 

 Thorson, are similar to the Point Barrow specimens (see pi. 25, fig. 4) 

 and to the shell shown in plate 19, figure 7. Schlesch's description 

 states (translation) : "The shell is oval with more or less rounded 

 posterior end and shows external fine and radiating striae. Super- 

 ficially it looks much like M. arenaria but the form of the hinge plate 

 shows that it stands next to M. truncata." 



Living specimens from Point Barrow show another similarity to 

 M. arenaria in that the sheath that extends onto the siphons is more 

 like that of M. arenaria, for it is not nearly so tough, wrinkled, and 

 extensive as in AI. truncata. 



Schlesch (1931) and Jensen (1901) report valves only, but Odhner 

 (1915) reports small living forma ovata from the Isfjorden in Spitz- 

 bergen. Soot-Ryen (1951) reports seeing small living M. pseudo- 

 arenaria from Spitzbergen, and in June 1927 and August 1930 he and 

 his companions collected 4 living specimens (ranging in length from 

 22.5 to 52 mm.) off the coast of Norway between lat. 69°56' N. and 

 lat. 67°8' N. 



M. pseudoarenaria is probably more abundant than collecting records 

 indicate. Equipment available at Point Barrow was incapable of 

 penetrating the substratum deeply enough to collect the larger 

 specimens of this species; the largest specimens (see collecting data 

 above) were either washed ashore by storms or were dredged at 

 Eluitkak Pass, where surging waters roll the rocks around and churn 

 up the mud sufficiently to expose some of the deeper mud-dwellers. 



Distribution: Point Barrow to Bellingham, Wash, (exact Pacific 

 records cannot be given until collections are reexamined with a view 

 to separating M. japonica and M. pseudoarenaria) ; Greenland, Iceland, 

 Spitzbergen, coast of Norway. 



