Shell, Shell and Sand, Imperial   Updated 12/15/2011
Imperial's Shell and Shell and Sand patterns are exactly the same except that the Shell and Sand has stippling between the shells as shown on the right. I suspect that when Imperial first released the Shell version it didn't sell well so they added the stippling to make the design more interesting. It's worth noting that some auctioneers may list either pattern as Shell, so check carefully.
Shell plates, 9 inches

Marigold, 575, 750 (both 2004),
   275, 375 (both 2006), 500 (2008)

Smoke, 650 (2004), 450 (2007), 200 (2009),
   325 (2010)

Shell bowls, about 7-8 inches

Amethyst, 155 (1997)

Blue, 2,800 (2004)

Marigold, 15-25

Smoke, 115 (2009), 40 (2010),
   55, 200 (both 2011)

Shell and Sand plates, 9 inches

Green, 275 (2004), 75 (2006), 135 (2007)

Helios, 45 (2010)

Marigold, 1,700 (2002), 800 (2003),
   950, 2,000 (both 2006)

Purple, 900, 1,050 (both 2008),
   425 (2011)

Purple, electric, 5,750 (2008),
   2,300, 2,400 (both 2011)

Smoke, 1,000 (2008), 1,500 (2009),
   700, 750 (both 2011)

Teal, 75 (2006), 85 (2007)

Shell and Sand bowls, 7-8 inches

Green, 40-60

Green, in metal frame, 170 (2006)

Helios, 20 (2005)

Lavender, 325 (2004), 215 (2006)

Marigold, 25-35

Marigold, pumpkin, 350 (2003)

Purple, 100, 125, 185, 205 (all 2010),
   65, 75, 80, 95, 125, 305 (all 2011)

Smoke, 225 (2004)

Teal, 225 (2004)