"Avicula, or Swallow, so called from the resemblance of the shells to a bird flying, was considered as a single species by Linnæus. Lamarck makes eighteen species in his new genera. Meleagrina has two species. The pearl-bearing muscle, as it is called, is found in the Persian Gulf, the Gulf of Mexico, &c. The interior of the shell is coated with thick pearl, and within it are formed those globular substances known by the name of pearls.
MELEAGRINA.
LIMA.
PECTEN.
"Family, Pectenida: genera—
| Pedum | Only species, from India, rare. |
| Lima | Ostrea. |
| Plagiostoma. | |
| Pecten | Ostrea, scallop. |
| Plicatula | Spondylus. |
| Spondylus | Spondylus, thorny-oyster. |
| Podopsis. |
"The genus Lima is longitudinal, auricled, or eared; hinge without teeth, with a hollow receiving the ligament. These are very pretty shells, generally white, almost transparent, resembling the Pecten. Lima comes from the American seas, and is a species easily obtained. There are also several fossil species.
"Plagiostoma is wholly a fossil genus, of which several species are found in this country, in lias, &c.
"The pectens are so easily known that I need only mention some fine species, such as P. pallium, a splendid shell, from the Indian seas: P. pleuronectes is a finely polished, smooth species from the Indian Ocean.
"The genus is divided into sections, viz. ears equal, ears unequal. You may find some common species on our own shores, and you may procure fossil species: they are numerous.