Very easy to muddle with Spisula discors but distinguishable in that S. discors, when the periostracum is missing is chalky white and often rusty while S murchisoni is often somewhat banded as in this specimen. Ring ridges are slightly finer and surface of fresh shells somewhat glossy. [S. discors lives in mud, this one in sand]
S murchisoni are also slightly more inequilateral when the two species are compared, with a marginally sharper angle on the longer side. There are also some technical differences in the hinge area.
Rabbit Island also happens to be the Type site for this sp.