The principal difference between the Anodonta and the Iridina, consists in the tuberculated hinge of the latter.
Shell. Thin, oval, much elongated, inauriculated; hinge very long, linear, and crenulated throughout its length, ligament external and marginal; two distinct muscular impressions. Inhabits the Nile and American coasts. Six species.
- Iridina exotica.
- I. Nilotica.
- · · · · ·
- I. cælistis.*
- I. rubens.*
- I. elongata.*
- I. McMurtria.*
FAMILY XIV.
Chamacea. Three genera.
1. Genus Diceras. Pl. [VIII].
Animal.
Shell. Inequivalve, adherent; beaks conical, very large, diverging in irregular spiral contortions; hinge with a large, thick, concave, subauricular tooth in the larger prominent valve; two muscular impressions. One species. Fossil.
- Diceras arietina.
2. Genus Chama. Pl. [VIII].
Animal. Body suborbicular terminated superiorly by a sort of hook; mantle very slightly opened for the passage of a foot, terminated at its extremity by a part much narrower than the base; superior lobes of the branchiæ very short.