Taken primarily from Kozloff, 1987, 1996 p.227 (Copyright 1987, 1996, University of Washington Press. Used in this web page by permission of University of Washington Press)
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| Lower taxonomic level | Main Page | Alphabetic Index | Systematic Index | Glossary |
| 1a | Without a pronounced groove separating most of the body whorl from its lower portion (up to about 3 cm high; usually blackish brown; common in some muddy bays to which it has been introduced from the Atlantic coast) | Ilyanassa obsoleta |
| 1b | With a pronounced groove separating most of the body whorl from its lower portion | 2 |
| 2a | Axial ribs priminent, but spiral ridges evident only on the body whorl (there are about 3 or 4 of them just above the groove) (up to about 1.5 cm high; introduced into a few bays in the Puget Sound region) | Nassarius fraterculus |
| 2b | Spiral ridges prominent on most whorls | 3 |
| 3a | Inner lip of aperture with a broad, usually orange callus that spreads out over the body whorl, well above the termination of the outer lip; axial ribs (which may or may not be prominent) not reaching the groove near the base of the body whorl; height up to 4.5 cm | Nassarius fossatus |
| 3b | Inner lip of the aperture without a large orange callus (if the callus spreads out over the body whorl, it does not go higher than the termination of the outer lip); axial ribs reaching the groove near the base of the body whorl; height rarely exceeding 3 cm | 4 |
| 4a | Axial ribs (of which there are more than 20) about equal to the spiral ridges, the two intersecting in such a way as to form nearly evenly spaced beads [the beads may not be visible without magnification] | 5 |
| 4b | Axial ribs (of which there are about 12) much more pronounced and more widely spaced than the spiral ridges (the two do not intersect in such a way that they form nearly evenly spaced beads) | Nassarius mendicus |
| 5a | Axial ribs generally not prominent, but the beads formed where they intersect with the spiral ridges are obvious without magnification; spiral ridges on body whorl all about the same size (there is no regular alternation of large and small ridges); height to about 3 cm (not likely to be found north of Oregon) | Nassarius rhinites |
| 5b | Axial ribs and spiral ridges about equally prominent, intersecting to form a cancellate pattern, but beading is not evident without magnification; spiral ridges on body whorl not all of the same size (larger ribs alternate with smaller ones); height to about 2 cm | Nassarius perpinguis |