294 



sides its widely remote habitat. It is much smaller and thinner, 

 its surface rude and dusky, instead of smooth and green ; its 

 outlines are all curves instead of right lines ; the dorsal and ter- 

 minal outlines form a continuous curve instead of a distinct 

 angle ; the beaks are more anterior and the cardinal apophysis 

 is never found in A. angidata, while it is constant in this. 



Anodon cognata. T. fragilis, transversa, oblongo-ovata ; 

 margine dorsali brevi, recto ; margine ventrali arcuato ; latere 

 antico rotundato ; latere postico oblique truncato, ad apicem rotun- 

 dato ; disco turgido ; epidermide virescente, nitido ; umbonibus 

 antemedianis inconspicuis, undulatis : margarita llvido-albida. 

 Long. 3 ; alt. i^ ; lat. 1 poll. Hah. Nisqually and near Fort 

 Vancouver. 



Resembles small specimens of A. cygnea ; but the dorsal 

 margin is shorter, not continuously straight, and forming an 

 abrupt angle above, anteriorly ; the posterior extremity is less 

 acute and more nasute ; the cavity of the beaks is also somewhat 

 over-arched. Excepting the beaks, it is like A. jiuviatilis. 



Alasmodon falcata. T. transversa, valde inequilateralis, fal- 

 cata, antice rotundata, postice deflecta, acuta marginibus subpa- 

 rallelis ; disco sub-excavato ; umbonibus obtusis, erosis ; epider- 

 mide subfusco ; dente cardinali in valva dextra elevate, trigono, 

 in v. sinistra longitudinali, compresso-triangulari ; margarita 

 purpurascente ; limbo argenteo. Long. 4 ; alt. 1 j- ; lat. 1 poll. 

 Hah. Wallawalla, Oregon ; Sacramento River, California. 



Mr. Lea and others have regarded this as a variety of A. mar- 

 garitifera; but besides the uniformly peach-blossom nacre, the 

 form is generally more arcuate, the exterior more waved, the 

 color darker, the anterior tooth in the right valve is comparatively 

 obsolete, longitudinally oblique and lamellar in the young. 



Unio famelicus. T. parva, tenuis, transversa, oblongo- 

 ovata, convexiuscula, epidermide fusco-castaneo induta ; mar- 

 gine dorsali arcuato ; margine ventrali rectiusculo ; latere antico 

 angusto ; latere postico oblique rotundato ; umbonibus baud ele- 

 vatis ad quadrantem anteriorem sitis ; dente cardinali obliquo, com- 

 presso, valido; dente laterali brevi, recto : margarita subpurpurea. 

 Long. 1^: alt. f ; lat. | poll. Hah. Wallawalla, Oregon. 



A small and rather remarkable species, like a miniature U. 



