S<7(f,o(o?3 Vol. 77, pp. 157-160 30 October 1964 PROCEEDINGS \ OF THE BIOLOGICAL SOCIETY OF WASHINGTON A NEW THRACIA FROM SOUTH CAROLINA ( Mollusca : Pelecypoda ) By Richard E. Petit Ocean Drive Beach, South Carolina In January of 1958 this writer found three specimens of Thracia in beach drift at low tide at Ocean Drive Beach, South Carolina. The specimens were alive when found. Although this is a very distinct species, description has been delayed in hopes that additional specimens would be found. However, no more living specimens have been seen to date. It is prob-able that this species is a borer in some soft material. Thracia morrisoni, n. sp. (Figs. 1-6) Shell irregularly ovate-quadrate, pure white, the undifferentiated umbones ending in small, inconspicuous beaks, nearly median in posi-tion, which touch at the margin, the right beak punctured by the left. The posterior side a little longer, gaping, subtruncated at the end. The anterior end broadly rounded. Valves are nearly equal, convex, the right a little larger. Surface shows a weak posterior umbonal angle, setting apart the posterior dorsal slope, that of the right valve carrying a radial rib near the margin. Surface sculptured with irregular concen-tric wrinkles, the whole covered with minute, hardly visible, sand-like granules. Hinge without teeth, ligament largely internal. External liga-ment very small, visible from above, resilium attached to a chrondophore in each valve, which project like a tooth behind an open cut or notch. Pallial sinus large, rounded, extending inward about one-third. Ventral margin smooth. Holotype (Figs. 1-6), U. S. National Museum catalogue number 635218, measures 13 mm high X 17.7 mm long. Diameter of both valves, 10.5 mm. One paratype (Fig. 4) measuring 11.2 mm high X 15.6 mm long, diameter of both valves 9.3 mm, has been placed in the Museum of Comparative Zoology, catalogue number 245145. Remaining paratype is in the Petit collection. This species is respectfully named for Dr. Joseph P. E. Morrison, Associate Curator, Division of Mollusks, U.S. National Museum. 16— Proc. Biol. Soc. Wash., Vol. 77, 1964 ( 157) '"smu^'oergfl^
BioStor
