FRESH WATER A^D LAND SHELLS. 47 



Shell smooth, elhptical, 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. Slcwartiana, (Nobis,) but is more rotund, more inflated and smoother 

 on the epidermis. In some of its characteristics, it approaches the An. Lhimmna, (Nobis,) 

 described in this paper. It differs from that in being less rotund, in having a smoother 

 and more polished epidermis, and it diff"ers entirely in the nacre, which is not salmon- 

 coloured, nor so thick or brilliant. 



Anodonta tortilis. pi. XXVIII. Fig. 54. 



Testa plicatd, obovatd, stibcompressd, inasguilalerali, e natibus minute lineatis; valuulis subtenuibus ; 

 natibus prominulis ; epidermide olivaced, minute tortile; margaritd cxruleo-albd 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 strire 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. crispata. 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 



