MARINE MOLLUSKS — MACGINITIE 153 



5 at 132 feet, 1 at 134 feet, 2 at 141 feet, and 1 at 477 feet. The 

 majority range between 25 and 35 mm. in length; the largest is 39.4 

 mm., the smallest is 13.9 mm. 



Other material examined: One specimen from the Barents Sea, 

 13 from Spitzbergen, 7 from Norway, 1 from Iceland, 2 from Disco 

 Bay, Greenland; 1 from Wellington Channel, Northwest Territories, 

 Canada (about lat. 76° N.), 5 from off Beachy Island, Labrador, and 

 5 from 60 fathoms, Labrador, and 1 from Massachusetts Bay; approx- 

 imately 50 from 18 stations from Kotzebue Sound to Plover Bay, to 

 Norton Sound, to Kamchatka, St. Matthew Island, Nunivak Island 

 and the Pribilofs; and 13 specimens (Stanford Collection) from deep 

 water off Humboldt Bay, Calif, 



Discussion: Yoldia hyperborea has not appeared in our Western 

 literature because it has been identified with Y. limatula (see Morris, 

 1947, pi. 1, fig. 5; 1952, pi. 1, fig. 8), some authors considering the 

 former merely an obtuse form of Y. limatula (Madsen, 1949, p. 20). 

 One of the difficulties appears to be the great variation in the propor- 

 tions of Y. hyperborea. Tj^pical adult Y. hyperborea are about twice 

 as long as high or even slightly less than twice as long as high, but 

 other specimens may be more than twice as long as high. These 

 latter specimens also have a more pointed posterior end than typical 

 Y. hyperborea, leading to confusion with Y. limatula and sometimes 

 with Y. sapotilla (see Abbott, 1954, pi. 27b). 



Ockelmann (1954) has made an analytical study of these 3 species 

 (and of Y. rnyalis) and as a result he erected a new subspecies of 

 Y. hyperborea, which he named limatuloides (Ockelmann, 1954, pi. 1, 

 fig. 2; pi. 2, fig. 2), characterized by the more pointed posterior end 

 and the length being more than twice the height. He also listed 

 distinguishing characteristics of the four species and the subspecies. 

 Neither Y. limatula nor Y. sapotilla (see Ockelmann, 1954, pis, 1, 2) 

 have a distinct sinuation in the anteroventral margin of the sheU, 

 whereas both Y. hyperborea and Y. h. limatuloides do have. In both 

 Y. limatula and Y. sapotilla the umbo is slightly in front of the middle, 

 but in Y. hyperborea and Y. h. limatuloides the umbo is somewhat 

 behind the middle. In contrast to Y. myalis, all of these have a 

 periostracum that appears varnished. 



In most of the specimens from Point Barrow, the length slightly 

 exceeds twice the height, but the excess is not so great as in Y. h. 

 limatuloides, nor is the posterior end sufficiently pointed for this 

 subspecies. 



In color the Point Barrow specimens vary from an olive straw 

 (those under 30 mm, in length) to a dark olive. The umbos and the 

 areas surrounding them are usually lighter colored than the remainder 



