The surfclam taxon Spisula solidissima similis, known as the “southern” surfclam and as Raveneli's surfelam, was recently shown to be reproductively isolated and genetically distinct from S. s. solidissima, the commercially harvested Atlantic surfclam, at the level of species. The reported distribution for S. s. similis includes shallow nearshore marine habitats south of Cape Hatteras as well as in the Gulf of Mexico. In contrast, S. s. solidissima is larger, has a longer life span, and is found in cooler waters north of Cape Hatteras both nearshore and offshore. The current study used molecular markers to test for S. s. similis in Long Island Sound (LIS), New York, at latitude 41°N, well north of its typical range. After analyzing a diagnostic mitochondrial DNA marker in 90 surfclam specimens from 3 locations in LIS, all samples were identified as S. s. similis. The LIS sample was also significantly different in both shell shape and in the shape of the cardinal tooth than comparably sized offshore S. s. solidissima. However, these shell differences are not adequate for differentiating between these taxa in the field. The documented history of Spisula in LIS is reviewed to address hypotheses about its origin there. In addition, the fishery management implications of our findings are discussed.