Key:  Family Littorinidae

Taken primarily from  Kozloff, 1987, 1996 p. 209 (Copyright 1987, 1996, University of Washington Press.  Used in this web page by permission of University of Washington Press)

Note:  Since the writing of Kozloff's key, Family Lacunidae has been included in Family Littorinidae as Subfamily Lacuninae
 

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1a	Diameter almost equal to the height; often with rather prominent spiral ridges (height up to about 2 cm; common, but mostly north of Oregon; primarily on rocky shores, but also on rocks, wood, and debris in bays and salt marshes	Littorina sitkana
1b	Height of shell decidedly greater than the diameter; without obvious spiral ridges	2
2a	Spire generally consisting of 3 whorls; usually with a white band inside the lower portion of the aperture, near the columella (color, except when the shell is eroded, usually brown or nearly olive, with irregular lighter mottling; not likely to be found north of Oregon)	Littorina keenae
2b	Spire generally consisting of 4 whorls; without a white band inside the aperture	3
3a	Shell thick (typical for Littorina); without an umbilicus; height to 1.5 cm; color usually dark brown, purple, or black, often with a checkerboard pattern of whitish areas or white streaks.  Common on rocky shores and also found on rocks in bays.  [Littorina plena, known to occur in Oregon and California, cannot be distinguished from L. scutulata based on these characters]	Littorina scutulata
3b	Shell thinner than typical for Littorina; with an umbilicus that is partly covered by the flangelike inner lip of the aperture; height to 8 mm; color brown (there are generally 2 or 3 wide, spiral bands of dark brown separated by narrow bands of lighter brown); restricted to salt marshes, where it is found on vegetation (Algamorda subrotundata in key)	Littorina subrotundata

  Littorina scutulata
  Littorina sitkana
  Littorina subrotundata