CHIEFLY OF THE UNITED STATES. 281 



valve; lateral teeth rather long, lamellar and somewhat curved; nacre bluish and 

 very iridescent. 



Proc. Acad. Nat. Sei. 1866, p. 133. 



Hah. — Siara, Thomas R. Ingalls, M.D. 



My cabinet. 

 Diam. -7, Length -9, Breadth 1-6 inch. 



Shell plicate, elliptical, inequilateral, somewhat biangular behind, rounded before ; 

 substance of the shell rather thin ; beaks a little prominent, folded at the tips ; 

 ligament short, thin and light brown; epidermis olive-green, shining, obscurely 

 rayed and with rather distant marks of growth; umbonial slope obtusely angular; 

 posterior slope narrow elliptical, with a slight carina and three green rays on each 

 valve, the upper one being obscure; cardinal teeth lamellar, somewhat oblique, 

 double in the right and single in the left valve ; lateral teeth rather long, lamellar 

 and somewhat curved ; anterior cicatrices confluent, rather large and very slightly 

 impressed; j)osterior cicatrices confluent, large and scarcely perceptible; dorsal 

 cicatrices placed immediately over the centre of the cavity of the beaks ; cavity of 

 the shell rather deep ; cavity of the beaks rather deep and angular; nacre bluish 

 and very iridescent. 



Remarlcs.— This is a small species which the late Dr. Ingalls sent me some years 

 since. In outline it stands between cairuleus and contradens (nobis), but is rather 

 shorter and stouter than either. The three specimens before me have a few irregular 

 undulations on the sides and some rather obscure ones on the posterior slope, which 

 distinguish it at once from the two above-mentioned species. In two of the species 

 the undulations are apparent on the inside. Other specimens very probably will be 

 found to be more plicate. Like the two cited species above, the cardinal teeth are 

 double in the right valve and single in the left. It is evident that the tips of the 

 beaks are furnished with folds, but they are too much eroded to make them out 

 satisfactorily. It cannot be confounded with Shurthffianus (nobis), which is much 

 wider, more cylindrical, more plicate and very much rougher. 



Unio pilatus. pi. 38, fig. 95. 



Testa Isevi, elliptica, valde infequilaterali, postice obtuse angulata, antice rotundata ; valvulis crassius- 

 culis, antice crassioribus ; natibus subprominentibus, ad apices minute undulatis ; epidermide 

 luteo-viridi, micanti, obsolete radiata; dentibus cardinalibus subcrassis, curtis, compressis, 

 crenulatis, in utroque valvulo duplieibus; lateralibus sublongis, subrectis- lamellatisque ; 

 margarita alba et valde iridesceute. 



Shell smooth, elliptical, very inequilateral, obtusely angular behind, rounded 

 before; valves somewhat thick, thicker before; beaks rather prominent, minutely 

 undulate at the tips ; epidermis yellowish-green, shining, obscurely rayed ; cardinal 



