THE NAIADES OF MISSOURI II3 



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 



9 215 X 118 X 84mm — 0.360 — (Mud Lake, Kenmoor, Mo.) 

 cf 155 X 80 X 66 " — 0.285 — (L. Contrary, St. Joseph, Mo.) 

 9 105 X 63 X 50 " — 0.380 — (" " " " ") 



9 16 X II X 5 " — 0.300 — (" " " " ") 



Several of these juvenile shells oi 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 jre-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 Naiades 

 is so polymorphic as A. grandis. Probably these mutations are 

 only zoogeographical 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 



