NAIADES OF MISSOURI 133 
half profusely and irregularly pustulate to smooth; beaks rather 
high, moderately inflated sculptured concentrically but faintly; 
epidermis dark straw to chocolate brown in color. 
INTERNAL STRUCTURES:—Cardinals heavy, irregular, double 
in each valve; inter-dentum broad, at right angles to laterals; 
laterals heavy, double in left, single in right; scars deeply impressed; 
umbonal cavities compressed by deep crevices; nacre usually white, 
irridescent especially posteriorly. 
Sex Length Height Diameter Um. ra. Locality 
O70) xs See x Ar imimin ono) (Plattes Ro) Avcency, Mo.) 
CueOOn xX. USO xe = Zour 0.300 (Grand R., Darlington, Mo.) 
OT A2 Xe One Xi 26) 0.295 (Platte R., Claire, Mo.) 
Chhley et Ry TAN OXiey Me 0.300 (Grand R., Utica, Mo.) 
Since schoolcraftensts is one of the greatest occurrence in 
individuals for this state, the writer has been able to secure the 
largest collection of its adolescent shells than any of the Nazades 
in Missouri. The above latter measurement is that of the smallest 
one but it was without bysst. Its general outline is more elongated 
than the mature shell, resembling the adult Q. quadrula, post- 
umbonal ridge more prominent, beaks fuller, almost drawn back 
to the center of dorsal line, characteristically painted with a 
bright, broad, fan-shaped, green ray at base of post ridge within 
the original shell area; beak sculpture indistinct, concentric, 
broken anteriorly by a radiating furrow directed out on disk. 
MISCELLANEOUS REMARKS:—The differences of this variety 
from the species has already been mentioned under the description 
of the genus. This form was not admitted by Simpson as a race 
and is merely referred as ‘‘a nearly smooth, compressed form of 
pustulosa.’’ The varieties of typical pustulosa, indeed, are great— 
especially as to disposition of pustules, etc., but this larger more 
characteristically quadrate form is so abundant in the north and 
west, where pustulosa-types are rarely found, that it surely deserves 
a separation into the subspecific, if not specific class. According 
to the figure and description that triangular variety found in 
the Ohio River, (that is, Lea’s pernodosa,) might be a synonym of 
schoolcraftensis. ‘Taking it all in all this subspecies is purely a 
geographical race, but may pass into normal form in a few places, 
even in the north and west, such as in the Mississippi River, 
Illinois and local points where clear water and swift streams are 
found. Schoolcraftensis is a lover of quiet, muddy situations, 
