120 THE AMERICAN. MIDLAND NATURALIST 
occupying all four gills, swollen in the center, when gravid, white 
when filled with ova, rich brown when charged with glochidia; 
conglutinates leaf-like, not solid, easily broken; glochidia semt- 
circular, medium in size, hinge line nearly straight, measuring 
0.205 x 0.215 mm. Dr. Surber kindly indentifies:—‘ Like plicata, 
but slighlty larger. Easily within the range of variation shown by 
this species from different localities.”’ 
SHELL CHARACTERS. 
EXTERNAL STRUCTURES:—Shell obliquely quadrate, small, 
moderately compressed, rounded before, usually biangulated 
behind; slightly alated; posterior half of disk profusely plicated, 
some plicated folds devaricated behind; slopes of post-dorsal 
ridge with several upcurved costae; beaks low well placed anteri- 
orly, sculptured in concentric fashion with strong ridges 
upcurved posteriorly; epidermis dark reddish brown to black, 
without rays. 
INTERNAL STRUCTURES:—Cardinals compressed, obliquely 
grooved, double in both valves, laterals long, slightly curved; 
beak cavities rather deep; nacre dull white. | 
Sex Length Height Diameter Locality 
9 a15” x Sox” 48mm (Osage R., Proctor, Mo.) 
SHLSO, XV eSSeexe Shi (White R., Hollister Mo.) 
ONE Oxi TiO ie Xun eS ast (Osage R., Monegaw Springs, Mo.) 
Coin PRC IN. <aMPY. Lois. hay Pe ‘“( * ” Taberville; Mo:) 
These last two measurements are among the smallest juvenile 
shells obtained from the Osage where quintardi is so abundant 
The writer has examined hundreds of them resulting in this gen- 
eral description:—Subovate, slightly longer than high, inflated 
(yet diameter never equal to height or length), rather bialated; 
beaks flat (dorsal line over umbonal region curved), sculptured 
quite well down on disk with three coarse irregular shaped ridges 
directed post-ventrad having comparatively deep valleys between 
these bars; epidermis brownish yellow; not byssiferous. Dr. 
Howard kindly comments: ‘‘These juvenile are of the plicata 
group of the Osage the exact relationships of which seems to be 
undecided.” 
MISCELLANEOUS REMARKS:—Surely this subspecies is a 
decided intergrade of the perplicatus Conrad and costata Rafinesque 
(=U. undulatus Barnes). Mr. Walker has referred this abundant 
shell for South and Central Missouri to perplicata variety quintardt 
