30 NAIADKS OF MISSOURI 



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 semi- 

 circular, medium in size, hinge line nearly straight, measuring 

 0.205 ^ 0.2TJ mm. Dr. vSurber 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 



9 115 X 80 X 48mm (Osage R., Proctor, Mo.) 



(White R., Hollister Mo.) 

 (Osage R., Monegaw Springs, Mo.) 

 ( " " 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 jtivenile are of the plicata 

 group of the Osage the exact relationships of which seems to be 

 imdecided." 



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 vSouth and Central Missouri to perplicata variety quintardi 



