Key:  Order Patellogastropoda Suborder Nacellina

Taken primarily from  Kozloff, 1987, 1996 p. 204 (Copyright 1987, 1996, University of Washington Press.  Used in this web page by permission of University of Washington Press)

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1a	Interior of shell uniformly white or faintly yellowish, without any dark markings; exterior whitish, unless it has a thin, light brown perostracum or is blackened by a deposit; apex at the end of the first one-third or slightly anterior to this; with delicate, scaly radial ribs or with threadlike striations that may have scales or beads where they are intersected by concentric growth lines (the striations are sometimes obscure, but at least a few of them should be visible when the shell is examined with the aid of 10x magnification); primarily subtidal in our region.	Lepetidae
1b	Interior of shell not uniformly white (it is either uniformly dark or has dark markings, such as an apical blotch, marginal band, or series of marginal streaks or spots; the only exception is Acmaea mitra, Acmaeidae, whose shell is nearly concial, with the apex close to the center); apex generally near the end of the first one-third, but sometimes considerably anterior to this, and sometimes central; radial ribs, when present, usually prominent and rather stout; mostly intertidal or shallow subtidal.	2
2a	Interior of shell uniformly white; exterior white (unless coated by an encrusting coralline alga, which is usually the case); shell nearly conical, about as high as wide, with the apex close the the center; without radial ribs.	Acmaeidae:  Acmaea mitra
2b	Interior of shell not uniformly white, exept in Niveotectura funiculata, Lottidae (it may be almost completely dark, or have an apical blotch, marginal streaks or spots); exterior rarely white, unless eroded by a fungus or abraded; shell not usually conical or as high as wide (there are exceptions); radial ribs present in some species.	3
3a	Height generally about one-fourth the length of the shell (but sometimes higher); margins prominently scalloped (the places where the pronounced radial ribs meet the margin may project as points); animal white, with dark spots on the head and sides of the foot.	Nacellidae:  Macclintockia scabra
3b	Height generally (but not always) more than one-fourth the length of the shell; margins not so prominently scalloped that the places where radial ribs meet the margin project as points (photo); animal sometimes white, but if so, without dark spots on the head and sides of the foot (includes most limpets of our region).	Lottiidae