264 THE AMERICAN MIDLAND NATURALIST 
rounded before, pointed behind; disk unsculptured; beaks full, 
apices recurved, sculptured by several coarse irregular double- 
looped ridges the loops being more or less nodulous; epidermis 
glossy, varied in color from brown-horn to green, growth lines 
rather undulated. 
INTERNAL STRUCTURES:—Hinge teeth completely lacking; 
muscle scars not well impressed, progressive impressions most 
evident; umbonal cavities large and deep especially in female 
shell; nacre variable naturally from whitish, or bluish to coppery 
or even to salmon chocolate or brick-red, irridescent. Probably 
the latter colors are more pathologic than normal. 
Sex Length Width Diameter Um. ra. Locality 
Q@ 215 x 118 x 84mm—o.360—(Mud Lake, Kenmoor, Mo.) 
oO 155 x 80 x 66 ”? —o.285—(L. fae St. escels Mo.) 
ONTOS) —X) 63h X 25007, —-0:380——C) te A) 
OW Oo se rie Exe eS5i 1-0-3000" wi # ") 
Several of these juvenile shells of A. grandis (the latter measure- 
ment being the smallest) were found in one spot on the west 
beach of Lake Contrary. These juvenile shells were indentified 
by Dr. A. D. Howard of the U. S. Fisheries, Biological Station, 
Fairport, Iowa, where experimental rearing of these species from 
the glochidium has been made and a series of shells have been 
obtained all the way from its larval to its independent and mature 
life. At the end of the fifth year it is identical with that of Lea’s 
opaca. The juvenile of the above measurement is very thin and 
papery almost transparent, is coarsely sculptured even on its 
disk—the bars being decidedly double-looped with a re-entering 
angle between the nodulous loops terminating at the tip of the 
umbone in two minute conical tubercles. It is especially to be 
noted that single laterals are faintly seen in each valve of this 
juvenile shell; also double right and single left cardinals may be 
seen with a (x12) lens. 
MISCELLANEOUS REMARKS:—Perhaps no species of Nazades 
is so polymorphic as A. grandis. Probably these mutations are 
only z6ogeographical expressions of its shell which seems to respond 
most readily to every change in ecological relations. Its pliable 
juvenile shell may be so shaped by its environment as to give 
rise to its many varietal forms. By choice grandis is lacustrine 
under which conditions its shell is typically inflated, shorter and 
thinner; if subjected even to the mild fluviatile action of a creek 
vt 
