94 THE CHICAGO ACADEMY OF SCIENCES. 
to the abdominal sac throughout their length; posterior part of 
the outer branchie becoming developed into a marsupium, con- 
sisting of distinct ovisacs whose lower ends are rounded; mar- 
supium rounded on its base and projecting below the inner 
ell. (Srmpson.) 7s 
Section LAMPSILIS (typical). 
GROUP OF LAMPSILIS VENTRICOSUS. 
26. Lampsilis ventricosds Barnes, pl. xii., figs. 3, 4, 5. 
Unio ventricosus BARNES, Amer. Jour. Sci. & Arts, Ist series, Vol. VI., p. 
267, figs. 14a, 14b, 14c, 1823. 
Unio accidens Lea, Trans. Amer. Phil. Soc., Vol. III., p. 485, pl. x., fig. 16, 
1829. 
Unio cardium RAFINESQUE, Conrad, Monograph of Unio, p. 7, 1884. 
Unio satur Lea, Trans. Amer. Phil. Soc., 2d series, Vol. X., p. 265, pl. 
xvii., fig. 19, 1852. 
Unio canadensis Lea, Jour. Phil. Acad., Vol. I1V., p. 268, pl. xliv., fig. 148, 
1859. 
Unio subovatus Lea, Reeve, Conch. Icon., Vol., XVI., Uvzzo, pl. Ixxxv., 
fig. 456 (not the true swdovatus). 
Shell: Large, inflated, subovate or elongately ovate, thick 
and heavy, rounded before and broadly rounded behind, the 
male being obtusely biangulate; dorsal margin slightly curved; 
ventral margin curved; surface smooth and polished, growth 
lines prominent; the height of the shell posterior to the umbones 
is very much greater than immediately in front of them; um- 
bones prominent, inflated, yellowish brown in color, marked by 
six coarse, elevated ridges; anterior umbonal slope short, rounded; 
posterior slope long, flat, forming a decided angle; ligament 
rather short, wide, stout, dark chestnut; epidermis yellowish 
or yellowish green, with a few rather wide (sometimes narrow) 
rays extending from the umbones to the ventral border (the 
posterior portion is almost without rays in some specimens); car- 
dinal teeth double in the left valve and single in the right, longer 
than wide, elevated, striated; the hinge line near the cardinal in 
the right valve is slightly enlarged, and may represent a second 
cardinal; lateral teeth strong, heavy, elevated, lamellar, crenu- 
lated, slightly curved; connecting bridge arched, narrow, 
smooth; anterior adductor muscle scar longer than wide, deeply 
excavated, especially near the cardinal teeth, striated; posterior 
adductor muscle scar rounded, as wide as long, concentrically 
striated, not much impressed; protractor pedis muscle scar wider 
than long, deeply impressed, coarsely striated; dorsal muscle 
scars situated on the posterior face of the cardinal teeth and the 
