Shell adhering, irregular, inequivalve, inequilateral, ostraceous; inferior valve rather more flat than the superior, divided at the summit into two sloping branches, whose approaching together forms a large oval hole, through which protrudes a muscle, the extremity of which becomes ossified and adheres to extraneous bodies; one sub-central muscular impression divided into three. Anomia ephippium. A. patellaris. A. cepa. A. electrica. A. pyriformis. A. fornicata. A. membranacea. A. squamula. A. lens. _A. ephippium._ The Saddle Anomia. Pl. 16, fig. 1. Shell sub-orbicular, irregularly wrinkled and waved; upper valve convex, under flat and perforated at the hinge, through which passes the ligament by which it is affixed to other bodies; inside pearly, and of various changing colours, such as green, purple, violet, and yellow. 6. Crania. The Scull. One species. So called from the appearance caused by three holes or cavities on the surface of the lower valve. Shell irregular, orbicular, inequivalve; the inferior valve almost flat, and marked on the interior with four muscular impressions, sometimes very deep, and of which the two sub-central are sufficiently connected to form but one; the superior valve like a Patella, more or less convex, with four very distinct muscular impressions, rather distant. _C. personata._ The masked Crania. Pl. 16, fig. 4. Orbicular; upper valve gibbous and conical, lower valve flat, with three perforations. FAMILY XX. BRACHIOPODA. Three genera. 1. Orbicula. One species. Greatly resembling a Patella, for which it is often mistaken on account of the lower valve being very thin, flat, and adhering. Shell sub-orbicular, very compressed, inequilateral, very inequivalve; the inferior valve very thin, adherent, and imperforated; the superior valve like a Patella, with a summit more or less inclined towards the posterior side. _O. Norwegica._ The Norwegian Orbicula. Pl. 17, fig. 4. Upper valve in the form of a depressed cone, with a summit produced and pointed. 2. Terebratula. Twelve species. Taken from the Anomia, and with great propriety, as its characteristic differences are very great; the perforation of the Anomia is always in the smaller valve, which is attached to the larger by a cardinal ligament, while in the Terebratula the perforation is always in the larger valve, which is connected to the smaller by teeth at the hinge. In some the valves are smooth, and in others grooved longitudinally.