Modiola Papuana. M. tulipa. M. albicosta. M. vagina. M. picta. M. sulcata. M. plicatula. M. semifusca. M. securis. M. purpurata. M. barbata. M. Guyanensis. M. Adriatica. M. pulex. M. discrepans. M. discors. M. trapezina. M. cinnamomea. M. silicula. M. plicata. M. semen. M. lithophaga. M. caudigera. _M. discors._ The discordant Modiola. Shell elongated oval, very convex, narrowest at the anterior end; striated at the two extremities; summit oblique; exterior greenish; interior white, with sometimes a pink-tinge, and somewhat pearly; crenulated margin. _M. Papuana._ The Papuan Modiola. Pl. 12, fig. 6. Species smooth, more or less triangular; summit near the anterior extremity; byssus obsolete in adults. _M. sulcata._ The furrowed Modiola. Species striated longitudinally. 3. Pinna. The Wing Shell. Fifteen species. This genus is the same as constituted by Linnæus; the shell is marine, generally very brittle and fragile, in form resembling an acute angled triangle; usually covered with longitudinal ribs and elevated transverse striæ; generally horn coloured. This genus is remarkable for the production of an abundant byssus of a fine brown silky texture, which the Italians frequently fabricate into articles of dress, equal in appearance to the finest silk. The Pinnæ often grow to a large size; they are sometimes found standing erect in the smooth-water bays, with the base of the shell uppermost, but generally affixed by the byssus to rocks and other sub-marine bodies. The filaments that compose the byssus are so tough and strong that the shells are not easily detached. Shell fibrous, fragile, regular, equivalve, longitudinal, triangular, base gaping and as if truncated; summit pointed and straight; hinge dorsal, longitudinal, linear, and without teeth; marginal ligament occupying almost the whole of the dorsal edge of the shell; one very broad muscular impression behind a trace of the anterior in the summit.