54 NEW UNIONID.E OF THE 



impressed; posterior cicatrices distinct and well impressed; dorsal cicatrices placed 

 under the plate between the cardinal and lateral teeth ; palleal cicatrices well im- 

 pressed; cavity of the shell deep and rounded; cavity of the beaks deep and angular; 

 nficre silvery white and very iridescent. 



Remarhs. — Half a dozen odd valves only were sent to me by the Smithsonian 

 Institution for examination. It reminds one of several very different species. In out- 

 line its quadrate form is almost identical with asj^errimus (nobis) ; but it has no 

 tubercles; in its emargination at base and on the posterior margin it resembles 

 hkmarginatus (nobis) ; in the epidermis, thickness and general aspect it reminds one of 

 Houstonemis (nobis), as well also petrvnusGovXA, but it is not rotund like those species, 

 and the lines of growth are closer. Some of the specimens are not so emarginate as 

 that figured. None were perfect enough to show the undulations of the beaks. Some 

 of the valves had small undulations on the posterior slope. 



This is one of the shells which Lieut. D. N. Couch, U. S. A. procured from Dr. 

 Berlandier's collection, and presented to the Smithsonian Institution. I name it after 

 him with great pleasure. 



Unio Popeii. pi. 66, fig. 197. 



Testa Irevi, transversa, eompresso-cylindracea, ad basim subemarginata, valde inoequilaterali, ad latere 



planulata, postice truncata ; valvulis subtenuibus, antic6 crassioribus ; natibus parvis, prominulis, ad 



apices granulatis ; epidermide vel tenebroso-olivi vel fusca, obsolete radiata ; dentibus cardinalibus 



compressis, erectis, acuminatis crenulatisque; lateralibus praelongis, lamellatis subrectisque ; margarita 



vel alba vel salmonis colore tincta et iridescente. 



Shell smooth, transverse, compresso-cylindrical, subemarginate at base, very 



inequilateral, flattened at the side and truncate behind ; valves rather thin ; thicker 



before ; beaks small, slightly prominent, granulate at the tips ; epidermis dark olive 



or brown and obscurely radiate ; cardinal teeth compressed, erect, acuminate and 



crenulate ; lateral teeth very long, lamellar and nearly straight ; nacre white or 



tinted with salmon color and iridescent. 



Proc. Acad. Nat. Sci. 1857, p. 102. 

 Hah. — Devil's River, Texas, and Rio Salado, New Leon, Mexico, Capt. Pope, 

 U. S. A. 



My cabinet and cabinet of Smithsonian Institution. 

 Diam. -6, Length 1-1, Breadth 2-3 inches. 



Shell smooth, transverse, compresso-cylindrical, subemarginate at base, very in- 

 equilateral, flattened at the sides and truncate behind ; substance of the shell rather 

 thin, thicker before ; beaks small, slightly prominent, granulate at the tips and nearly 

 terminal ; ligament long and rather thin ; epidermis dark olive or brown, obscurely 

 radiate and with rather close lines of growth ; umbonial slope slightly raised and 

 obscurely angular; posterior slope raised into a carina and with two impressed lines 



