154 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 109 



of the shell; this is especially marked in the larger, darker specimens 

 (pi. 18, fig. 5). 



The specimens I examined from north of the Pribilofs appear to be 

 Y. hyperborea and, with the exception of the 13 specimens of this 

 species from deep water off Hmnboldt Bay, those from south of the 

 Pribilofs appear to be Y. limatula. Unfortunately, my examination 

 and notes were made before Ockelmann's study was published, so 

 that I cannot give separate ranges for typical Y. hyperborea and the 

 subspecies liinatuloides. However, I did examine typical Y. hyper- 

 borea: 11 from Spitzbergen, 1 from the Barents Sea, 10 from Labra- 

 dor, 2 from 175 fathoms from Disco Bay, Greenland. Since the 

 height was less marked than in t}T)ical Y. hyper-borea, the specimens 

 I examined from Norway, Iceland, and Massachusetts Bay may very 

 well be the subspecies limatuloides or transitional stages between it 

 and Y. hyperborea. 



A specimen 40 mm. long from Spitzbergen has 8 or 9 growth cessa- 

 tion lines and several secondary lines, one 31 mm. long has 6 or 7 

 lines, and one 29 mm. long has 8 lines; one 32 mm. long from Bergen, 

 Norway, has 6 or 7; and one 21 mm, long from the Wellington Channel 

 has 6 or 8 lines. 



Distribution: Point Barrow south to the Pribilofs, and off Hum- 

 boldt Bay; Wellington Channel, Jones Sound, Smith Sound, Labrador, 

 and Massachusetts Bay; the eastern Siberian Ice Sea, the Kara Sea, 

 Novaya Zemlya, the White Sea, the Murman Coast, the Barents Sea, 

 Spitzbergen, Norway, Iceland, and Greenland. 



Yoldia scissurata Dall, 1898 



Yoldia scissurata Dall, 1898, p. 595. 



One shell 31 mm. long by 17 mm. high was taken at 141 feet, and 

 a left valve 23.5 mm. long by 12.5 mm. high was washed ashore on 

 Aug. 21, 1949. 



Other material examined : Seven specunens from northern Japan 

 and over 75 from localities ranging from Point Barrow south through 

 Bering Sea and the Sea of Okhotsk to Bristol Bay, the Aleutians, 

 Sitka Harbor, and the coast of Washington. 



Discussion: Grant and Gale (1931, p. 131) suggest that Y. scis- 

 surata Dall and Y. ensifera Dall are synonymous. I find the following 

 differences between the two species: Y. scissurata is higher anteriorly 

 and is proportionately longer from the umbos to the anterior end and 

 proportionately shorter from the umbos to the posterior end than 

 Y. ensifera. The posterior dorsal blades of the valves are longer and 

 much higher in Y. ensifera than in Y. scissurata, so that a line from 

 the beaks to the end of the rostrum always cuts across the blades in 

 Y. ensifera but seldom does in Y. scissurata. The rostrum is more 



