FRESH WATER AND LAND SHELLS. 75 



Shell smooth, elliptical, inflated, rounded before and behind; substance of the shell 

 rather thick; beaks somewhat prominent, nearly terminal; ligament rather long and thin; 

 epidermis yellow, somewhat polished, smooth, with small rays; cardinal teeth double in 

 both valves, erect, pointed; lateral teeth long, nearly straight, lamellar; anterior cicatrices 

 distinct; posterior cicatrices confluent; dorsal cicatrices placed across the centre of the 

 cavity of the beaks; cavity of the shell rather deep and rounded; cavity of the beaks 

 deep and angular. 



Remarks. — Dr. Hale has twice sent me this shell, from the Red River, and I have now 

 four specimens before me. I thought when I first received a specimen, some years since, 

 that it was a variety of Hydiana, but it diflers from that species in being much less pon- 

 derous, in the beaks being more terminal, and in being less rayed. These are also 

 smaller. The rays arc stronger on the posterior slope. One of the specimens is rayed 

 nearly over the whole disk — another has rays only on the posterior part. 



Unio caperatus. PI. V. Fig. 14. 



Tesla Ixvi, obliqua, eompressa; valvulis crnssis; nalibus elcvatis; epidermide rvfo-fusru; dentibus cardi- 

 nalilius percrassis; laleralibus tongis, a cardinalibut scparatis, crassis curvisque; margnritd alba. 



Shell smooth, oblique, compressed; valves thick; beaks elevated; epidermis reddish-brown; cardinal teeth very 

 thick; lateral teeth long, (being separated from the cardinal teeth,) thick, and curved; nacre white. 



Hab. Clinch River, Tennessee. President Estabrook. 



My cabinet and cabinets of Mr. Estabrook and Dr. Foreman. 

 Diam. 1.2, Length 1.9, Breadth 2 5 inches 



Shell smooth, oblique, compressed, flattened on the umboncs, very inequilateral, surface 

 of the shell thick, thinner behind; beaks elevated; ligament rather long and thick; epider- 

 mis reddish-brown, wrinkled, with numerous, irregular, capillary rays; cardinal teeth very 

 thick, large, and disposed to be double in both valves; lateral teeth long, (being separated 

 from the cardinal teeth,) thick, curved, and enlarged at the posterior end; anterior cica- 

 trices distinct; posterior cicatrices distinct; dorsal cicatrices placed under the plate near 

 tin cardinal tooth; cavity of the shell shallow; cavity of the beaks deep and angular; 

 nacre white 



Remarks. — I have three specimens of this interesting species before me. They are all 

 mature shells, and a good deal eroded. It belongs to that group of which the U. irroratus, 

 (Nobis,) may be considered the type, having the correlative characteristics. It will stand 

 between irroniins and dromas. From the first it differs in being oblique, and more com- 

 pressed — from tin latter in being smaller, flatter, and not having the- humps on the 

 ombones. The capillary rays seem to spread over the whole disk, but the specimens 

 being old and worn, that notable character is nearly obliterated. The colour of the epi- 

 dermis in younger specimens, will no doubt be found to be greenish and yellow, and the 

 rays very beautiful, as in the irroratus. Two specimens of the three have a tint of salmon- 

 colour in the nacre of the posterior portion The plate from the beak to the margin, 

 between the cardinal and lateral teeth, is large and flat, and the space between the two 

 teeth very much arched. It is very evident, from the line- of growth, that the young 

 arc nearly round, the disk becoming protruded and patulous, when old. 



