152 PROCEEDINGS OF THE NATIONAL MUSEUM vol. io» 



and in the degree of truncateness. In the var. lutescens the keel 

 appears to be slightly higher near the umbos than in the typical form. 



A specimen 16.5 by 10.7 by 6.9 mm. from the "Arctic Ocean" shows 

 7 distinct growth cessation lines (much darker than the surrounding 

 areas of the shell) with a narrower secondary line between some of 

 these; another, 20.1 by 13.6 by 9.8 mm., shows 9 distinct growth 

 cessation lines with a few secondary lines; still another, onlj^ 15.9 mm. 

 long, shows 11 or 12 nearly equally strong lines. 



Distribution: Collinson Point and Point Barrow, Alaska; Well- 

 ington Channel, Canada, south to Greenland; also Spitzbergen and 

 Norway. 



Yoldia myalis (Couthouy, 1838) 



Plate 18, figure 1 



Nucula myalis Couthouy, 1838, p. 62, pi. 3, fig. 7. 



Yoldia myalis Gould, 1870, p. 160, fig. 467.— Oldroyd, 1924, p. 30, pi. 5, fig. 8.— 



Abbott, 1954, p. 340, pi. 27d.— Ockelmann, 1954, p. 18, pi. 1, fig. 5; pi. 2, 



figs. 5, 10. 



Approximately 35 specimens were taken from 18 stations at depths 

 ranging from 72 to 453 feet: 12 were taken from 213 feet, 1 from 453 

 feet, 1 from 295 feet, 1 from 246 feet, and 1 from 204 feet, the re- 

 mainder coming from depths of less than 200 feet, with from 1 to 3 

 specimens per station. 



Other material examined: Over 100 specimens from localities 

 ranging from Cape Smythe, Alaska, to the Aleutians, southeast 

 Alaska, and Puget Sound; also over 25 specimens from Nova Scotia, 

 Maine, and Massachusetts. 



Discussion: The fossette varies in depth and in shape, being short 

 and triangular in some specimens and longer and narrower in others. 

 The pallial sinus may be rounded or truncate at the anterior end and 

 it may or may not be long enough to reach to a vertical line extended 

 from the beaks. Some shells are much heavier than others. 



Distribution: From Point Barrow to Puget Sound; from Hudson 

 Strait to Massachusetts. 



Yoldia hyperborea Torrell, 1859 {ex Loven, MS.) 



Plate 18, figure 5 



Nucula hyperhorea Loven, MS. 



Yoldia hyperborea Torrell, 1859, p. 149, pi. 2, figs. 6a-b.— Odhner, 1910, p. 18, pi. 

 1, fig. 23.— Ockelmann, 1954, p. 8, pi. 1, figs. 1, 2; pi. 2, figs. 1-4. 



About 14 living specunens and several valves were collected, the 

 living ones as follows: 1 at 10 feet (Sept. 8, 1949), 1 at 70 feet, 1 at 72 

 feet, 1 at 80 to 100 feet (Aug. 21, 1948), 1 at 120 feet (Sept. 8, 1949), 



