NEW CNIONID/E OF THE UNITED STATES. 77 



behind and round before, nearly equilateral; substance of the shell rather thick, 

 thicker before ; beaks somewhat prominent, pointed and corrugate at the apex ; liga- 

 ment rather large, somewhat long, and light brown ; epidermis reddish brown, very 

 obscurely radiate, with two or three very distant marks of growth ; umbonial slope 

 well raised and angular; posterior slope somewhat carinate, narrow, with two slightly 

 impressed lines from the beaks to the posterior margin ; cardinal teeth rather large, 

 striate, somewhat compressed and crenulate ; lateral teeth rather thick, somewhat long 

 and nearly straight ; anterior cicatrices distinct, somewhat large and well impressed ; 

 posterior cicatrices distinct, rather large and slightly impressed ; dorsal cicatrices 

 situated within the cavity of the beak under the plate; cavity of the shell rather 

 shallow and wide; cavity of the beaks deep and angular; nacre sometimes white, 

 generally pinkish and iridescent. 



Remarlcs. — I have before me seven specimens of various ages of this interesting 

 species, which I owe to the kindness of my energetic and assiduous friends Dr. 

 Showalter, of Alabama, and Dr. Spillman, of Mississippi. On the first receipt of 

 two specimens I thought that they presented a remarkable sulcate variety of rubi- 

 ginosus (nobis), having the exact outline of that species, and a general aspect which 

 allies them closely. But on the receipt of younger specimens, with perfect beaks, 

 I found that important region exhibited a totally different arrangement. The rvhigi- 

 nosus has only two or three small subconcentric folds with nodes along the angle of 

 the umbonial slope, while the negalus has the whole region of the beak covered with 

 corrugate folds, in one of the young specimens reaching down the sides for three- 

 quarters of an inch, reminding one forcibly of the corrugations on the well known 

 species cormgatus, Lam., from India. It is allied also to ruhldus (nobis,) which ac- 

 companied it ; but that species, while it is sulcate usually all over, as this is, is much 

 more inflated, and has a much darker epidermis. Of the seven specimens before me, five 

 are rosaceous in the nacre, one is white, and one reddish salmon. There is much dis- 

 position in the lateral tooth of the right valve to be double. In some of the specimens 

 it is quite so. 



Unio glandaceus. PI. 9, fig. 226. 



Testa Isevi, subtriangulari, inflata, inrcquilaterali, postieo subbiangulata, an tied rotunda t&; valvulis crassis, 

 antice crassioribus ; natibus prominulis, crassis; epiderimde glandacea, rugos:l, eradiatfi; dcutibus 

 cardinalibus magnis, valde sulcatis, erectis ; lateralibus curtis, crassis, corrugatis, obliquis subrcctisque ; 

 margarita alba et iridescente. 



Shell smooth, subtriangular, inflated, inequilateral, subbiangular behind, rounded 

 before; valves thick, thicker before; beaks somewhat prominent, thick; epidermis 

 reddish-brown, rough, without rays; cardinal teeth large, very much sulcate, erect; 



20 



