82 THE CHICAGO ACADEMY OF SCIENCES. 
19. Quadrula undulata Barnes, pl. xxii., fig. 1, 2; pl. xii., fig. 1. 
Unio undulatus BARNES, Am. Jour. of Sci. and Arts, Ist series, Vol. VI., 
p- 120, fig. 2, 1823. 
Unio costatus RaFINESQUE, Conrad, Monograph of Unio, p. 17, pl. vii., 
1836. 
Unio latecostatus Lea, Trans. Am. Phil. Soc., Vol. X., p. 68, pl. i., fig. 2, 
1845. 
Unio pilsbryi Marsu, The Nautilus, Vol. V., p. 1, 1891; Vol. VII., pl. i., 
figs. 7, 8, 1893 (vide Call). 
Shell: Quadrately elliptical, undulate, compressed, very 
thick and heavy, rounded before and obtusely triangular 
behind; dorsal margin straight, ventral margin slightly rounded; 
surface roughened by lines of growth which are raised into thin 
scales on the ventral border; umbones'‘not elevated, somewhat 
inflated, brownish horn color, marked by five coarse, diverging, 
rounded ridges; anterior umbonal slope short, rounded; poste- 
rior slope long, flatly rounded; ligament long, narrow, thick, 
reddish or blackish horn color; epidermis reddish brown or 
blackish; the whole surface of the shell is marked by coarse 
undulations extending in a diagonal] direction across the surface, 
in most specimens bifurcating; five or six large undulations are 
generally present with several smaller ones; cardinal teeth 
double in both valves, about equal in the left, and the anterior 
much the smaller in the right valve, all but the latter heavy, 
thick, triangular, diverging, very deeply striated and grooved; 
lateral teeth long, thick, more or less elevated, slightly 
curved ventrally, serrated; connecting plate between the teeth 
thick, flat, smooth; adductor muscles and frotractor pedis 
scar as in p/icata; dorsal muscle scars numerous, of good 
size, deeply pitted, situated on the posterior face of the 
cardinal tooth and on the under side of the connecting plate; 
pallial line very deeply impressed, crenulated; cavity of the 
beaks broad, shallow; nacre silvery white, iridescent on the 
posterior portion. 
Length, 131.00; height, 88.00; breadth, 52.00 mill. (9321). 
86.00; es 65.00; ‘ 33.00 ‘ (9347). 
83:00;; .*? 60.00; . 31.50 * (9526). 
a 150:00;) ,-%:) 108,00; = 60.00 *' (coll. Jensen). 
Animal: Creamy white, light brown on abdomen and upper 
portions; anal and branchial openings large, the former slightly 
crenulated and the latter with numerous small papillz; poste- 
rior part of mantle yellowish brown, edged with black, 
especially near the two siphons; liver darker in color than the 
