According to Buffon, this bird is sometimes seen perched on floating trees in the rivers of Guiana and Cayenne. * * * * * * [Illustration: Anodon, _Pl. 1_ _A. areolatus_.] ANODON areolatus. _Areolated Horse Mussel._ ---- GENERIC CHARACTER. See Unio, Pl. 1. (Anodon. Iridina. Dipsus. _Auct._) ---- SPECIFIC CHARACTER. _Shell transversely oval, not winged, umbones small, ventricose, not touching; with a short undulated projection of the hinge margin in one valve, and a corresponding concavity in the other; both placed beneath the umbones._ ---- The principal character of _Anodon_, rests on the absence of teeth; the _A. anatinus_, common to our rivers and ponds, being taken as the type of the group. But, as Nature steps progressively, in her departure from one form, and in her advance to another, so among the Anodons we find several shells, which do not strictly exhibit the typical character; and these we shall briefly notice. In the sketch already given of this group, we have placed the genus _Anodon_ between _Iridina_ and _Alasmodon_. The _Iridina nilotica_ Sow, "has scarcely any appearance of crenations along the hinge line," but for this, it consequently would present a simple lamellar ridge, extending nearly the length of the shell; such, in short, as is seen in _Dipsus plicatus_ (Leach), whose tooth may be so described. By this shell we are led to _A. rubens_ Lam. where a lamellar plate, though much shorter, is placed beneath the umbones. _Iridina Cailliandi_ perfectly resembles _A. rubens_, except in being without any vestige of this plate. We have now entered among the typical species, where every form occurs between a round and an ensiform shape. Leaving these, Nature proceeds to fashion an indistinct developement of _Alasmodon_ in the species before us, where that part of the hinge plate, immediately beneath the umbones, is somewhat raised, and undulated. In _A. rugosus_ these compressed undulations assume more the form of tubercles; and finally, in the _Alasmodon marginatus_ of Say, the teeth are sufficiently developed to place that shell in a distinct group. Our esteemed and accomplished friend, Mrs. Corrie of Birmingham, favoured us with two examples of what appears to be a variety of that which we have figured. The substance of both is opake; the inside white, tinged with buff, and with scarcely any pearly lustre. Inhabits North America, but we know not any precise locality. * * * * * * [Illustration: MITRA. Pl. 2. _1. strigata. 2. bicolor. 3. carinata._] MITRA strigata. ---- SPECIFIC CHARACTER. _Shell very smooth, chestnut with paler longitudinal stripes, which are white at their commencement; aperture white, shorter than the spire; pillar 4-plaited_. Mitra strigata. _Sw. in Brand's Journ., No. 33, p. 37, Ap. 1824._ ----