Hab. in Africæ interioris fluvio Gammaroo.
The form of the cardinal callosity to which the semi-internal ligament is attached affords a distinction sufficiently characteristic of the species: its oblique truncating plane, which extends towards the rather indistinct umbo, is, in the closed state of the shell, in partial contact with that of the corresponding and similarly formed callus of the other valve. The general form of the shell is oblong or rounded, but appears to be subject to considerable variation: one of the specimens before me exhibits the exterior of Lamarck’s A. transversa, which latter is no doubt a casual variety only of the other species described and figured by that naturalist.
These shells are externally furnished with a blackish-brown epidermis; beneath this a white film is deposited, on the removal of which a beautiful pearly naker appears, similar to that of the internal surface of the valves. The blistered appearance of the interior of both the valves is constant in all specimens, and may, as intimately connected with the structure of the shell, be considered of sufficient importance to be admitted into the distinctive character of the genus.
Lamarck, imagining that these shells live at the bottom of the sea, named the genus, as he says, after one of the daughters of Oceanus. Though the Ætheriæ are now well known to be fluviatile shells, the emendators of zoological nomenclature may still be exonerated from framing a new name for this genus, since the old one is derivable from the original locality of its species; a part of central Africa having, according to Pliny, been anciently known by the appellation of Ætheria.
The second shell, a new species of Iridina, may be thus characterized:
Iridina Oudnæi: testa transversa ovato-lanceolata tumidiuscula, cardine stricto sub-edentulo, basis margine sinuato.
Hab. cum priore.
This species is very distinct from E. elongata in form and in the hinge line being without crenulation; and from E. nilotica, which it resembles in the latter of those characters, it differs by its form, inferior thickness, and iridescence. The length of the specimen before me is 4⅔, its greatest breadth at the umbo nearly two inches. Placed on the basal edge, which is concave, the anterior side presents a considerable slope from the umbo to the exterior margin, which gives the valves a tapering or ovate-lanceolate form. The external epidermis, of a greenish-brown colour, exhibits slightly undulating striæ of growth. The interior surface is slightly uneven-undulated, white, with delicate opalescent colours, green and faint pink; the former chiefly disposed in spots. The muscular impressions are more slightly marked than in the other species.
For the third shell, which I considered as a new species of Anodon, I propose the name of
Anodon Clappertoni: testa transversim oblonga, antice in extremo cardine acute excisa.