Variety equivalents:
Judd 1407 = Pollock 1550 =
Adams-Woodin 1449

Designer:
Obverse: William Barber
Reverse: William Barber

Rarity: Very Rare

Metal content: Silver

Edge: Plain

Patterns for a Twenty Cents coin were first proposed in 1874, in response to a request from Western states, whose populace held non-silver coins in disdain yet complained that they did not have enough coins to make small change!  The new denomination was authorized by the Act of March 3, 1875 and production began on May 19, 1875.

All the pattern designs of 1875 were created by William Barber, who adopted a nautical theme for the year.  His "Sailor Head" design (Judd 1392-1395) lost out to the Seated Liberty design, which matched stylistically the coins already being produced by the Mint.

Images courtesy of Superior Galleries

Significant examples:
PCGS Proof-64 (illustrated above).  Ex - Superior Galleries' "Pre-Long Beach Sale", October 1-3, 2000, Lot 4427, where it was described as follows:  "Judd-1407, Pollock-1550. Silver. Plain Edge. With lovely deep golden brown to splashes of blue, both sides choice and blemish-free. Similar to the regular obverse but the date is smaller; reverse has 1/5 OF A DOLLAR in a laurel wreath."

Sources and/or recommended reading:
"United States Pattern, Experimental And Trial Pieces" by J. Hewitt Judd, M.D.

"United States Patterns And Related Issues" by Andrew W. Pollock III