Parvamussium pailoloum (Dall, Bartsch & Rehder, 1938)
DALL, W. H., P. BARTSCH & H. A. REHDER. 1938. A manual of the Recent and fossil marine pelecypod mollusks of the Hawaiian Islands. Bernice P. Bishop Museum Bulletin, 153: i-iv, 1-233, pls. 1-58. [p. 82, pl. 19, figs. 8-11; pl. 20, figs. 5, 6]
1938 Propeamussium pailoloum Dall, Bartsch & Rehder, 1938
W. H. Dall, P. Bartsch & H. A. Rehder, 1938, plates 19, 20.
|
«Shell small, alabastine, with the radiating internal ribs showing through as white streaks. The basal portion of the right wing of the right valve is narrowly notched to accommodate the byssus. The part posterior to this bears seven feeble radiating threads and a broad cord at the summit, all of which are crossed, as well as the byssal area, by concentric laminae which form a series of strong scales on the dorsal border. The posterior wing of the right valve is shorter than the anterior and shows no ribs, only feeble slender, closely approximated, concentric laminae. The prodissoconch is smooth and the portion immediately following it is smooth but soon develops slender concentric threads which increase in strength toward the ventral margin and which are separated by spaces about as wide as the threads. The spaces between these concentric threads are marked by numerous microscopic axial lirations which are seen only under high magnification. The anterior wing of the left valve shows no radiating cords but numerous, somewhat irregular, slender, but well elevated lamellae. The posterior wing is much shorter than the anterior and marked by much feebler lamellae. In fact here they are almost threads. The prodissoconch here, as in the right valve, is smooth, the part succeeding marked by concentric threads which increase in strength until in the latter two thirds of the shell they are presented by very slender, very thin, wavy lamellae which are about one eighth as wide as the spaces that separate them, becoming again concentrated toward the ventral margin. The hinge is very narrow. The dorsal border of the anterior wing of the right valve is denticulated, the rest of the border is smooth. The byssal notch is narrow and but feebly developed. The interior of the shell shows 10 radiating ribs with a little intercalated piece between the last two posterior cords.
The type, U.S.N.M. Cat. No. 173209, was dredged by the U. S. Bureau of Fisheries Steamer Albatross at Station 3866 in Pailolo Channel in 283-284 fathoms, on gray mud and fine sand bottom; bottom temperature 43.8° F. It measures: height, 9.2 mm.; length, 9.5 mm.; diameter, 3.2 mm.
This species is easily distinguished from the other Hawaiian Propeamussiums by lacking radiating ribs on the left valve and by having ten internal ribs.» WILLIAM HEALEY DALL, PAUL BARTSCH & HARALD ALFRED REHDER, 1938
|