THE NAIADES OF MISSOURI 1 29 



ductive as far as able to determine from sterile material that is 

 only at hand. Glochidia not known. 



SHELL CHARACTERS. 



External Structures: — vShell elongate - elliptical moder- 

 ately inflated, obtusely rounded before, pointed behind, dorsal 

 line acurate, ventral with a slight long upward curve ; disk smooth : 

 post-umbonal ridge rounded; beaks low, faintly sculptured con- 

 centrically across two radiating ridges; epidermis olive green or 

 yellowish rayed with capillary lines, some arranged in bundles. 



Internal Structures: — Cardinals double in both valves, 

 post-cardinal of right valve rudimentary; interdentum long, 

 rather narrow, notched; scars well impressed; beak cavity shallow 

 branchial, however, large with deep impression in female shell; 

 nacre white to pearl blue. 



Sex Length Height Diameter Locality 



9 95 X 50 X 28 (Spring R., Webb City) 



9 86 X 44 X 25 (White R.. Hollister) 



c? 85 X 45 X 24 (Jack's Rork, Shannon Co.) 



9 60 X 30 X 17.5 (White R., Hollister) 



This last specimen being yotmg and well preserved shows 

 the fine characteristic rays more distinctly and while the beak 

 sculpture would show more distinctly than in older shells yet it 

 is even obscure here and does not add anything to the above 

 description of the external shell structures. 



MiscELLANELUS REMARKS: — Before Simpson had studied 

 the soft parts of this species he had considered it as E. dilatata 

 {=U. gibbosus); however, its peculiar marsupial characters would 

 not only discriminate, but also its different beak sculpture and 

 dissimilar hinge. The beak sculpture of dilatata is one of the most 

 emphatic among the Naiades while that of this species is one of 

 the most obscure ; besides the interdentum of the former is broader 

 and thicker while the branchial impression of clintonensis dis- 

 tinguishes it from all other species outside of its genus. This 

 species lies very close to its fellow, facsiolaris, and it is considered 

 by some as merely a variety of it, but perhaps it is a good species 

 on account the lack of the splotched rays and larger, heavier, 

 thicker shell of the type for Ellipisaria. ' Clintonensis is abundant 



' Recent studies by Dr. Ortmann and Mr. Frierson have resulted in 

 the positive conclusion that the Unio occidentalis Conrad (Monog., VII, 



