EXOTIC I'NIONID.I?. ")n 



ala posterioris basi.apiccfjuc undulatis, natibus comprcssis, ad apiccm undulatis, baud prominentibus; 

 opidermidc nitida, tcnebroso-vividi ct totii radiata ; dentibus oardinalibus parviusculis, eompressis, in 

 utrnque valvulo duplieibus et ecrnuis ; lateralibus longissimis, lamellatis subcurvisf(ue; ligamento 

 oolatn ; margarita alba ct valde iridescente. 



Shell double winged, plicate, triangular, very much compressed, angular be- 

 hind, very inequilateral ; posterior wing high, acuminate, crenulate on the margin ; 

 valves rather thin, connate before and behind the beak ; beaks compressed, not 

 prominent, undulate to the tip ; the base and summit of the posterior wing undu- 

 lated ; epidermis shining, dark green radiated all over ; cardinal teeth rather 

 small, compressed, double in both valves and inclined downwards ; lateral teeth very 

 long, lamellar and somewhat curved ; ligament concealed ; nacr^ white and beauti- 

 fully iridescent. 



Unto Cumlnijii, Lea. Froc. Acad. Nat. Sci., Vol. ti, p. 54. 



Ilah. — Northern part of China. H. Cuming. 



My cabinet and cabinet of Mr. Cuming, London. 

 Diam. 1, Length 4-5, Breadth 5-2 inches. 



Shell double winged, folded on the side and behind the umljonial slope, triangular, 

 very much compressed, angular behind, very inequilateral; posterior wing high, 

 acuminate, crenulate on the superior margin ; anterior wing very small and slightly 

 elevated; substance of the shell rather thin, connate before and behind the beaks ; 

 beaks, as well as the base and summit of the posterior wing, undulated ; compressed, 

 undulated at tip, not prominent ; ligament concealed ; epidermis smooth and shining, 

 dark green, radiated all over, even to the extremity of the wing, with distant marks 

 of growth ; umbonial slope slightly elevated and rounded ; posterior sloi^e raised into 

 a high wing ; cardinal teeth rather small, compressed, double in both valves and 

 inclining downwards ; lateral teeth very long, lamellar and somewhat curved, single 

 in the right and double in the left valve ; anterior cicatrices small, the superior and 

 lateral smaller ones both distinct from the large one ; posterior cicatrices confluent 

 and indistinct ; dorsal cicatrices small, placed obliquely across the cavity of the beak ; 

 pallial cicatrix well impressed and very distant from the margin of the disk ; cavity 

 of the shell extremely shallow ; cavity of the beaks scarcely jjerceptible ; nacre white 

 and richly iridescent. 



Remarks. — This very beautiful and rare Unio is, in form and general outline, very 

 much like the Dijisas jylicaUi-s, Leach, but they cannot be confounded with each other, 

 a.s they belong to very distinct genera, the Dijysas having but one linear tooth in 

 each valve, while the above de.scribed shell has perfectly well defined, compressed, 

 cardinal teeth, double in both valves. It also has long lateral, lamellar teeth, double 

 in the left and single in the right valve. It diflers also in the folds, having them 

 extending over the flattened side from the beaks, becoming lower and more obscure 



