REPORT ON THE UNIONDAE OF ST. JOSEPH RIVER 9 
The shell of this species is elliptical in outliue, rather thick and 
heavy. It is rounded anteriorly and obtusely angulated posteriorly. 
The dorsal margin is straight in both sexes; the ventral margin is 
straight in the male and curved in the female. The lines of growth 
are quite heavy and form strong wrinkles on the dorsal part of the 
posterior angle. The umbones are eroded on all specimens in this 
collection, and all are marked by three almost straight, elevated 
ridges. The ligament is long, narrow and dark brown horn colored. 
The epidermis is yellowish-green to dark brown or black. The 
cardinal teeth are thick and heavy, pyramidal and striated on the 
upper surfaces. The lateral teeth are undeveloped and appear as a 
slight thickening of the hinge plate. The anterior adductor muscle 
scar is very wide, slightly impressed and iridescent. The pallial 
line is impressed only on the anterior portion of the shell. The 
cavity of the shell and of the beaks is shallow. The nacre is silvery 
white, bluish white or salmon colored. Old shells have a dark 
purple band along the entire margin of the valve. ’ 
ALASMIDONTA MARGINATA (Say). 
Alasmodonta marginata Say, Nich. Encyc., 1819, 1, Jl. Ac. Nat. Sci. Phil. I. 
1819, P. 459. 
Margarita (Margaritana) marginata Lea, Syn., 1836, p. 43. 
Alasmodonta marginata Baker, Moll. Chi. Pt. I., 1898, p. 62, pl. IV, fig 4: 
WAG Sie SRD CSD Sheers 
Unio Marginatus Sowerby, Conch. Icon., XVI, 1866, pl. LI, fig. 267 
Alasmidonta truncata Simpson, Syn., 1900, p. 671. 
This species should be easy to recognize on account of its heavy 
shell, inflated umbones that are characteristically marked with 
three very coarse, undulating ridges, and its truncated posterior 
border. The ligament is wide, not very long and of a very dark 
horn color. The epidermis is brownish or greenish with wide dark 
rays extending from the umbones to the ventral border, and dotted 
with black spots and dashes. The cardinal teeth are thin, elevated 
and striated; there is one in the right and two in the left valve. The 
lateral teeth are simply a thickening of the hinge. The anterior 
muscle scar as also the protractor are marked by lines of growth. 
The posterior muscle scar is only slightly impressed. The cavity 
of the shell is deep; that of the beaks is shallow. The pallial line 
is wellimpressed. The nacre is a bluish white, pearly ae iridescent, 
especially on the edges of the valves. 
