10 PEOCEEDINGS OF THE NATIONAL MUSEUM vol. 75 



ELLIPTIC COMPLANATUS 



Plate 4, figs. 1 to 10 



SHELL 



Plate 4, figs. 1, 2, and 4 



The shell of Elliptio complanatus has an elongate trapezoidal shape, 

 with the dorsal and ventral margins nearly parallel. The posterior 

 ridge which is well developed and generally double, ends in a point at 

 the base, while the anterior end is rounded. 



The surface of the shell is marked by irregular growth lines which 

 are smooth in the young shell and rough in the old. In color it 

 ranges from tawny green to greenish brown. 



In E. complanatus there is no marsupial bulge distinguishing the 

 female shell. The interior may be white, straw-color, salmon, or 

 various shades of purple. 



In the left valve there are two nearly straight lateral hinge teeth 

 and two irregular pseudocardinals, while in the right valve there is 

 one lateral hinge tooth and one stumpy pseudocardinal with a faint 

 one above it. 



From the base of the anterior adductor scar just in front of the 

 pallial line impression, there is a delicate groove which passes down- 

 ward and curves around the base of the shell representing the 

 course of the mantle artery. 



MANTLE 



Plate 4, fig. 3 



The only variation in the mantle is a heavier pigmentation at the 

 siphons. The anterior and posterior adductor muscles are very 

 large with the anterior muscle assuming a distinct quadrilateral shape. 

 The body is roughly trapezoidal in shape. 



GILLS AND REPRODUCTIVE SYSTEM 



Plate 4, figs. 1, and 9 



The gills are semicircular with the marsupium occupying the entire 

 outer gills. 



The glochidia are bookless. 



BEAK SCULPTURE 



Plate 4, fig. 5 



ELLIPTIC PRODUCTUS 



Plate 5, figs. 1 to 10 



SHELL 



Plate 5, figs. 1, 2, and 4 



The shell is elongated, ranging in color from dark reddish brown 

 to olive green and is rather thin. The beaks, which in the adult 

 shell are generally eroded, are low. In very young shells there is a 



