THE NATURAL HISTORY SURVEY. 85 
regular, pulsations thirty-one to thirty-three per minute. Four 
gills used as marsupia. 
Distribution: ‘Western New York to Kansas and Minne- 
sota, and south to Texas and Alabama. (Call. ) 
Geological distribution: Pleistocene. 
Habitat: Found in the larger lakes and rivers, on a muddy 
or sandy bottom, in somewhat shallow water. 
Remarks: This is a characteristic and somewhat rare 
species in this area, and it is one of our most beautiful Unios. 
The pustulate character of the posterior margin is quite unique, 
some of the larger pustules being shaped like the nodules in 
Obliguaria rejiexa. So far as known, it is confined to the south- 
ern region, and the specimens are of medium size, yellowish 
green faintly rayed with grass green. In old specimens the 
shell becomes a dark chestnut brown. 
GROUP OF QUADRULA PUSTULOSA. ~ 
21. Quadrula verrucosa Barnes, pl. xxiii. 
Unio verrucosus BARNES, Amer. Journ. Sci. and Art, lst series, Vol. VI., 
p. 123, fig. 6, 1823. 
Shell: Ovately quadrate, thick, heavy, pustulate, com- 
pressed, rounded before and squarely truncated behind; dorsal 
margin nearly straight, ventral margin generally rounded but 
sometimes nearly straight; surface strongly roughened by 
growth lines and profusely covered with tubercles and pustules 
on all but the anterior portion, the pustules being wider than 
long and following the direction of the growth lines; the pus- 
tules are more numerous in the center of the shell than else- 
where; umbones small, prominent but not elevated, somewhat 
inflated, strongly directed anteriorly, brown in color, marked by 
numerous heavy, wavy ridges, which extend for a considerable 
distance toward the ventral part of the umbonal slope; anterior 
umbonal slope rounded, posterior flat, somewhat alate, or 
slightly excavated, forming a shoulder; ligament long, wide, 
stout, very dark horn color; epidermis uniform dark brown; 
cardinal teeth single in the right and double in the left (there 
is almost always a very small tooth-like projection in the right 
valve, near the lunule, which is without doubt a rudimentary 
second cardinal), flattened, large, solid, triangular, deeply 
grooved, diverging in the left valve; lateral teeth short, very 
strong, striated, directed ventrally; connecting bridge broad, 
flat, smooth and solid; the shell extends above and posterior to 
