hard clam vs round clam

hard clam and round clam both are nouns.

Word	Noun	Adjective	Verb	Adverb
hard clam	Yes	No	No	No
round clam	Yes	No	No	No

As nouns, hard clam and round clam are synonyms defined as:

hard clam and round clam: an edible American clam; the heavy shells were used as money by some American Indians

Other synonyms of hard clam include hard-shell clam, Mercenaria mercenaria, quahaug, quahog, Venus mercenaria.

hard clam (noun)	round clam (noun)
an edible American clam; the heavy shells were used as money by some American Indians	an edible American clam; the heavy shells were used as money by some American Indians
	Atlantic coast round clams with hard shells; large clams usually used for chowders or other clam dishes