Species grooved, with the summit or heel of the large valve deeply hollowed even to the edge of the articulation; the slope rounded; the valves sub-bilobate by the apparent slope of the anterior edge.
3. Lingula. One species.
The valves of this genus are united by means of a tubular, fleshy, or membranous peduncle surrounding the narrow part of them, and of which the base is affixed to marine substances.
Shell covered with epidermis, sub-equivalve, equilateral, depressed, elongated, truncated anteriorly, summit middle and posterior, without trace of ligament, but supported at the extremity of a long fibro-gelatinous peduncle, which attaches it vertically to sub-marine bodies; multiple muscular impression.
L. anatina. The Duck’s-bill Lingula. Pl. [17], fig. 2.
Covered with a green, shining epidermis, shaped like a duck’s bill, and having a cylindrical peduncle.
CLASS IV.
MOLLUSCA.
TWENTY-TWO FAMILIES.
FAMILY I.
Pteropoda. Six genera
Some genera of this family are without a testaceous covering, and are mentioned only for the sake of preserving the family entire.