Scott No.: 171
Date of Issue: May 16, 1963
Species: Mountain Chicken (aka Giant Ditch Frog) (Leptodactylus fallax)
Yeah, I was wondering why it's called the "Mountain Chicken," too. Answer: it's very big (up to 21 centimeters) and is hunted for food. It's also on the list of critically endangered species. Wikipedia has a pretty good article on the species, including the fact that the males have a spur on their thumbs, which they use to grab the females.
*Scott No: 178
Date of Issue: May 16, 1963
Frog in Coat of Arms
*Scott No.: 218
Date of Issue: July 8, 1968
Overprint of Scott 171, "Associated Statehood"
*Scott No.: 225
Date of Issue: July 8, 1968
Overprint of Scott 178, "Associated Statehood"
Scott No.: 232
Date of Issue: November 3, 1968
Overprint of Scott 178, "National Day, 3 November 1968"
The frog is in the coat of arms, in the upper right corner.
*Scott No: 285
Date of Issue: November 26, 1969
Frog in coat of arms
*Scott No.: 310
Date of Issue: December 28, 1970
Set: Centenary of the Red Cross, frog in coat of arms
Scott No.: 391, 394
Date of Issue: May 4, 1974
Set: Centenary of Dominican postage stamps. The stamp depicts the first stamp issued by Dominica and the coat of arms (frog in the upper right corner). In the other stamp in the series, the stamp image is accompanied by a map of the island or a post horn.
*Scott No.: 605
Date of Issue: November 3, 1978
Set: Independence; frog in coat of arms
*Scott No.: 1271
Date of Issue: December 13, 1990
Set: Christmas, Disney characters on carousel animals
Scott No.: 1451
Date of Issue: May 18, 1992
Set: Christopher Columbus/flora and fauna
Species: Crapaud Frog/Mountain Chicken (Leptodactylus fallax)
Scott No.: 2168j (minisheet)
Date of Issue: November 9, 1999
Set: Fauna
Species: North American Bullfrog (Rana catesbiana)
*Scott No.: 2258, 2260
Date of Issue: December 18, 2000
Set: Wildlife
Species: Puerto Rican Crested Toad (Peltophryne lemur), Panamanian Golden Frog (Atelopus Zeteki)
*Scott No.: 2816
Date of Issue: November 18, 2020
Set: Wildlife of Dominica*
Species: Mountain Chicken (Leptodactylus fallax)
*Scott: 2821c, 2821 (minisheet)
Date of Issue: November 18, 2020
Set: Wildlife of Dominica
Species: Mountain Chicken (Leptodactylus fallax)