Explanation of Plate 19 



Fig. 1. — Panomya arctica (Lamarck) from Unimak Pass in the Aleutians, exterior of right 

 valve. 



Figs. 2, 3, 5. — Pseudopythina compressa Dall washed ashore Aug. 27, 1949: 2, e.xterior of 

 right valve, showing spinules on dorsal margin; 3, exterior of left valve; 5, interior of 

 left valve. 



Fig. 4. — Chlamys islandica (Miiller) from 420 feet: left, exterior of left valve; right, exterior 

 of right valve. 



Figs. 6, 8. — Mya japonica Jay: 6, Ball's lectotype of Mya intermedia, from Chignik Bay 

 (east side of the Alaska Peninsula), showing extreme development of anterior end and 

 pallial sinus; 8, from Tokyo Bay, Japan (from the Stanford Collection), showing 

 pallial sinus no deeper than that of M. arenaria. 



Fig. 7. — Mya pseudoarenaria Schlesch from the Arctic (Sta. 24, Canadian Arctic Expedi- 

 tion), a specimen formerly assigned to M. intermedia. 



Magnification: 1, X .33; 2, 3, 5, X 2.8; 4, 6, X .46; 7, X 1.4; 8, X .35. 



