132 THE AMERICAN MIDLAND NATURALIST 
MISCELLANEOUS REMARKS:—Typically this species is a small 
shell, very upright with beaks protruding extremely anteriorly 
and with irregularly arranged pustules over its disk. In this 
latter character it is separated from Q. nodulata with which it 
is often confused; then too nodulata is not so rotund. Pustulosa 
is more typically a southern shell while its variety, schoolcraftensis, 
is more of a northern and western form. Its favorite home is clear 
water and rather swift streams and is associated with Q. sphae- 
rica, refulgens, mortont, etc.,—all of which are not found in Missouri; 
on the other hand its northern relative (schoolcraftensis) is more 
of a lover of mud bottom and sluggish current. It is strange that 
this species is not found in South Missouri where its ecological 
conditions are most favorable; however, it is not at all common 
anywhere in the great South-west. It is occasionally found in 
Central Missouri but mostly in varietal forms. The Mississippi 
River is the only locality for anything like its type. It should 
be a species of wide distribution since its host distributor is the 
common crappie (P. annularis). 
Quadrula pustulosa schoolcraftensis (Lea). 
(‘“Warty-Back,”’ ‘‘ Pimple-Back.’’) 
Pl. XVII. Figs. 42 A—D. 
1834— Unio schoolcraftensis Lea, Tr. Am. Phil. Soc., V., p. 37, pl. III, 
fig. 9. 
ANIMAL CHARACTERS. 
NUTRITIVE STRUCTURES:—Branchial opening large, low, with 
short arboreal papillae; anal obscurely crenulated; supra-anal 
closely connected to anal but not deciduous; gills tilted at an 
abrupt angle, inner laminae of inner gills entirely free from visceral 
mass; palpi unusually long, somewhat curved; except brownish 
gills and palps the soft parts are dull whitish or tan. 
REPRODUCTIVE STRUCTURES:—All four gills marsupial, septa 
crowded, ventral edges pointed and distended slightly in center 
when gravid; conglutinates white with thin, transparent spots 
arranged transversely in rows; glochidia same in form as the 
parent species, but a little larger (0.235 x 0.320). 
SHELL CHARACTERS. 
EXTERNAL STRUCTURES :—Shell large, subquadrate, ventral mar- 
gin gently curved, moderately inflated, thick, heavy; posterior 
