Simplistrigilla in the western Atlantic Ocean (Mollusca, Bivalvia)

In a recent monograph on the tellinid genus Strigilla, the absence of a representative of the subgenus Simplistrigilla was noted in the Western Atlantic region (Boss, 1969). Simplistrigilla was described by Olsson (1961) with the species S. strata Olsson, 1961, as type. The species is rare with a considerable range in the Panamic Province of the eastern Pacific Ocean, occurring from El Lagartillo, Panama, southward to Punta Blanca, Ecuador. The unusual feature possessed by this species is in the nature of the scissulae or oblique incised lines which descend across the shell from the anterior dorsal margin toward the ventral and posterior margins. In S. strata these scissulations do not change direction or form a complex of flexures along the posterior dorsal surface of the shell, whereas all other species of Strigilla possess a variously flexed sculpture. Using this peculiarity of sculpture, Olsson established Simplistrigilla and he also noted that the larval shell or the nepionic surface of the umbo in S. strata is relatively large, distinct, lacking the scissulate sculpture and having extremely fine, hair-like concentric sculpture. Scissulate sculpture itself, known to be diagnostic for most taxa of Strigilla, has arisen independently in several tellinoid lineages (Boss, 1966) and has been shown to have functional significance in that it facilitates burrowing (Stanley, 1969; 1970). A sample collected by the H. N1. M. S. "Luymes" off Suriname during the program of Research of the Continental Shell of Suriname (Onderzoek Continentale Plat Suriname) was sent to me by Mrs. Hanneke Nijssen-Meyer and proved to be a new species of Simplistrigilla. I had earlier segregated what I took to be aberrant specimens of Strigilla mirabilis (Philippi, 1841) which