Explanation of Plate 20 



Figs. 1, 3-7, 9-11. — Montacuta planata (Dall): 1, a proup of 4 specimens from Greenland; 

 3, a group of 4 specimens (USNM 159303) of Dall's cotypes of Mysella -planata from 

 Plover Bay; 4, embryos from a specimen (4.5 x 3.4 x 2.0 mm.) from 328 feet, Point 

 Barrow, Alaska; 5, a group of 3 specimens (USNM 333648) of Dall's Mysella molleri 

 (Morch) from Greenland; 6, Dall's figured type of Mysella planata (USNM 159310) 

 from the Shumagins; 7, portion of right valve of a specimen from 477 feet, Point Barrow, 

 Alaska, with thinner shell, and smaller hinge structures than No. 6, being possibh" a 

 variant of Montacuta planata; 9, right valve of M. planata from 477 feet; 10, 11, views of 

 interiors ot specimens from Greenland (10, showing the resilium in place; 11, showing 

 the hinge without the resilium). 



Fig. 2. — Axinopsida orbiculata (G. Sars) from 120 feet (Aug. 8, 1949). 



Fig. 8. — Diplodonta aleutica Dall, ju\'eiiile from 741 feet. 



M.agnification: 1, 3, 5, 10 X 4.6; 2, X 6; 4, X 17.7; 6, 9, X 4.5; 7, X 6.1; 8, 11, X .44. 



