THE PEN SHELLS. SEA WINGS. FIN SHELLS - FAMILY PINNIDIE. Genus PINNA, Linn.
Shell equivalve, wedge-shaped, oblique, thin, fragile, and generally scaled; hinge lateral, toothless; umbones terminal anterior; ligament in long groove; mantle double-fringed; foot long, spinning strong cord. Osphradium developed into a finger like process that can be extended beyond the shell margin. Large genus in warm seas of Old and New World.
The Rude Pen Shell (P. rudis, Linn.) is irregular in growth, blistery, whitewashed on the orange-red surface. Semi-tubular scales, large and few, adorn the indistinct radiating ridges toward the margin. Length, 8 to to inches.
Habitat. West Indies.
The Noble Pen Shell (P. nobilis, Linn.) shows a startling crowded array of erect, recurving prickly scales pointing in various directions, on the outer portion of its triangular shell. The tapering stem is scantily set with scales. The ground colour is olivaceous at the umbo becoming rosy as it spreads outward. The scales are yellowish. Length, 6 to 7 inches.
Habitat. Mediterranean.
The Pen Shell (P. seminuda, Lam.) is covered with erect, delicate scales, that follow the lines of growth. On the outer posterior area they are largest and are set on radiating lines. Forward and approaching the umbones the scales become gradually so minute and worn down that the apical half is bare. This shell is thin, of smoky, transparent, horny texture lined with pearl. The lips meet in a straight line. Length, 6 to 10 inches.
Habitat. North Carolina southward.
The Prickly Pen Shell (P. muricata, Linn.) Is triangular, with straight lips and incurving side lines. The obscure ribs are 40 I The Pen Shells. Sea Wings. Fin Shells set with erect, open, triangular scales. The horny shell sub stance is white and semi-transparent. Length, 6 to 8 inches.
Habitat. North Carolina to West Indies.
The Black Pen Shell (P. ni gra, Chemn.) spreads widely from a narrow beak, and is constantly black. It rounds at the lips. One specimen may be small and show a formidable array of semi-tubular scales erect on the radiating ridges. Others, remarkable for size, are smooth. Length, 6 to 15 inches.
Habitat. South Seas and Philippines.
The Philippine Pen Shell (P. Philippinensis, Henley) is a greatly elongated, narrow, straight-lipped Pinna with smooth, pearly surface. Its colourless ground shows narrow smoky streaks. Length, 8 to 12 inches.
The Rough Pinna (P. rugosa, Sby.) is a strongly ribbed and extravagantly tubercled species. The outline widens abruptly from the narrow, stem-like umbonal region to the front, which bears semi-tubular, leaf-like scales that twist very irregularly. Colour, dark smoky. Length, lo to i8 inches.
Habitat. In sand banks, Panama Bay.
The Moor Pinna (P. M aura, Sby.), dark brown to black, its posterior half covered with regular lines of similarly curving tubular scales, is another handsome Panama species. Length, 6 to 8 inches.