Key to Family Epitoniidae

Taken primarily from  Kozloff, 1987, 1996  p. 217 (Copyright 1987, 1996, University of Washington Press.  Used in this web page by permission of University of Washington Press)

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1a	With a spiral ridge near the base of the body whorl (the axial ribs may or may not terminate at this ridge)	2
1b	Without a spiral ridge near the base of the body whorl (the axial ribs continue to the base of this whorl)	3
2a	Usually with 7 axial ribs (intertidal and subtidal) Opalia chacei Strong, 1937 and O. wroblebskii (Morch, 1876) are synonyms.	Opalia borealis
2b	With 8-10 axial ribs (intertidal and subtidal)	Opalia montereyensis
3a	Generally with more than 20 axial ribs (range 19-30) (height to 2.2 cm; subtidal)	Nitidiscala catalinensis
3b	Generally with fewer than 20 axial ribs (Nitidiscala sawinae sometimes has 20 or 21)	4
4a	Height about twice the diameter, or only slightly more than twice the diameter, but not as much as 2.5 times the diameter (with 11-13 axial ribs; height up to 1.7 cm; subtidal)	Nitidiscala caamanoi
4b	Height usually considerably more than twice the diameter (generally 2.5 to 3 times the diameter)	5
5a	Generally with not more than 14 axial ribs	6
5b	Generally with more than 14 axial ribs (with as few as 10, however, in Nitidiscala indianorum)	7
6a	With 8-14 axial ribs; upper portions of whorls usually with a brownish or purplish band just below the suture; axial ribs evenly curved, neither angular nor with projections near the sutures (length up to 1.5 cm; common intertidal and shallow subtidal species feeding on the sea anemones Anthopleura elegantissima and Anthopleura xanthogrammica) (Nitidiscala tincta in key)	Epitonium tinctum
6b	With 7-14 axial ribs; upper portions of whorls without a brownish or purplish band below the suture; axial ribs often angular or with a spine just below the suture (length up to 2.6 cm; intertidal and subtidal) (Nitidiscala hindsii in key)	Epitonium hindsii
7a	Axial ribs decidedly angular just below the sutures, and sometimes with a spine (with 12-20 axial ribs; length up to 1.8 cm; subtidal)	Nitidiscala catalinae
7b	Axial ribs evenly curved, not angular just below the sutures (spines may or may not be present)	8
8a	With 14-21 axial ribs; spines generally present on the axial ribs just below the sutures; height up to 2.4 cm (subtidal)	Nitidiscala sawinae
8b	With 10-17 axial ribs; spines rarely present on the axial ribs; height up to nearly 4 cm (intertidal and subtidal) (Nitidiscala indianorum in key)	Epitonium indianorum

  Epitonium tinctum
  Opalia montereyensis