niPLOnON 1251 



Unio fontainianns HANUiv, Biv. Shells, 1856, p. 3.84, pi. xxi, 



fig. 27. — SowKRRY, Conch. Icon., XVI, 1868, pi. lxxxvii, 



fig. 466. 

 Mojrgaron (Unio) fontainianns Lua, Syn., 1870, p. 56. 

 Diplcdcn fontainianus Simpson, Syn., 1900, p. 886. 

 Unio fontaineana d'ORBiGNY, Voy. Am. Mer., 1B43. P- 605, 



pi. LXix^ figs. 6, 7. 



The type -is a young shell. The species seems to show a 

 good deal of variation in minor characters such as details of 

 form, color and the like, but all the shells T have seen are 

 wedge-shaped in front when viewed from above and all have 

 elongated, compressed pseudocardinals. Those in the left 

 valve are sometimes double, but often more or less united. 



Var. deer pins n. v. 



Shell unevenly obovate, subinflated, rather solid ; left valve 

 with two radial, short pseudocardinals, which are often split 

 up into a number of denticles, with two remote laterals ; right 

 valve with two pseudocardinals, the upper smaller, the lower 

 often split up, and behind it there are often small denticles on 

 the hinge plate, with one granular lateral. 



Guahyba, Brazil. 



I have before me a large number of specimens of this form 

 and a number of others, which I refer to the var. o;i'atHs. 

 Both vary considerably and seem to differ constantly only in 

 the character of the pseudocardinals. In fontainianns and 

 gratns they are long and compressed, both are more commonly 

 united in the left valve and though sometimes roughened they 

 are never divided. In the form I have called deceptns the 

 pseudocardinals are short and much split up. they are usually 

 more or less radial and there are generally a number of den- 

 ticles behind those of the right valve. Young shells show these 

 characters as well as the old ones. 



Var. grains (Lea). 



Shell more decidedly wedge-shaped in front than the type 

 when viewed from above ; epidermis smoother, lighter colored 

 and suibshining; post-dorsal wing a little more angled behind. 



Uruguay River, South America. 



