FRESH WATER AND LAND SIIELLS. AT 
Shell smooth, elliptical, very much inflated, inequilateral, subangular behind, angular at 
the anterior dorsal margin, very much inflated and somewhat gibbous on the umbones, 
nearly straight on the dorsal line; substance of the shell thin; beaks prominent, very much 
swollen and rugosely wrinkled at the tip; ligament rather short and somewhat thick ; 
epidermis green, polished, slightly striate, obscurely rayed, with three rather obscure rays 
on the posterior slope, and with distant marks of growth; posterior slope very wide, 
_ rather short, and rather depressed; umbonial slope rounded, with an irregular, slightly 
raised line from the beaks to the posterior margin; anterior cicatrices confluent; posterior 
cicatrices confluent; dorsal cicatrices invisible; palleal cicatrix not observable; cavity of 
the shell very deep and rounded; cavity of the beaks deep and rounded; nacre white and 
iridescent. 
Remarks.—Several specimens are before me, of different ages. It is perhaps most 
nearly allied to An. Stewartiana, (Nobis,) but is more rotund, more inflated and smoother 
on the epidermis. In some of its characteristics, it approaches the An. Linneana, (Nobis,) 
described in this paper. It differs from that in being less rotund, in having a smoother 
and more polished epidermis, and it differs entirely in the nacre, which is not salmon- 
coloured, nor so thick or brilliant. 
Anoponta Tortinis. Pl, XXVIII. Fig. 54. 
Testa plicatd, obovata, subcompressd, inequilaterali, é natibus minute lineatis; valvulis sublenuibus ; 
nalibus prominulis; epidermide olivaced, minute tortile; margarita ceruleo-alba et iridescente. 
Shell plicate, obovate, somewhat compressed, inequilateral, minutely lined from the beaks; beaks a little 
prominent; valves rather thin; epidermis olive, minutely wreathed; nacre bluish-white and iridescent. 
Hab. Carthagena, South America, J. C. Trautwine, Esq. 
My cabinet. 
Diam. .5, Length .9, Breadth 1.4 inches, 
Shell plicate, obovate, somewhat compressed, inequilateral, rather obtusely rounded 
before and subalate behind, with a minute line from the beaks to the posterior margin ; 
substance of the shell rather thin; beaks a little prominent, submedial; ligament rather 
long and thin; epidermis olive, minutely wreathed nearly over the whole disk, without 
rays; umbonial slope compressed and elevated into a carina; anterior cicatrices confluent ; 
posterior cicatrices confluent; dorsal cicatrices none; cavity of the shell rather shallow; 
cavity of the beaks very shallow and subangular; nacre bluish-white, iridescent, with 
minute striz from the beaks to the margin. 
Remarks.—It is to be regretted that only a single specimen of this shell should have 
been found by Mr. Trautwine, to whose kindness I owe the possession of it. It is 
remarkable for the minute wreaths of the epidermis, which are distributed in festoons 
over most of the disk. In these wreaths it resembles the An. erispata, Lam., which is the 
only species of the family I have seen with this singular character. The specimen before 
me has the beaks beautifully tinged with a greenish hue, being epidermal matter deposited 
between the layers of nacreous matter. In the cavity of the beaks this shows quite con- 
spicuously, and is stronger in two divergent lines. Under the lens, in this specimen, a 
