144 THE NAIADES OF MISSOURI 



writer; however, the nutritive structures of the males are identical 

 with those of N. ligamcntina and cllipsiforniis. 



SHELL CHARACTERS. 



External Structures: — Shell sub-elliptical, rather thin, 

 smooth, somewhat compressed, rounded before, obtusely angular 

 behind; beaks rather low, sculptured by three or four fine shaped 

 undulations; epidermis brown polished horn, with numerous green 

 capillary rays, disposed mostly posteriorly and showing through 

 the thin shell on the inside. 



Internal Structures: — Cardinals small, single in right, 

 double in left valve, erect and parallel with laterals; left inter- 

 dentum cut away for post-cardinal tooth; beak cavities rather 

 shallow; nacre bluish, copper}^ or salmon in umbonal cavity. 



Sex Length Height Diameter LocaHty 



cf 55 X 21 X 13 mm (White R., Hollisterj 



cf 35-5 X 21.5 X 13.5mm ( " " " ) 



c? 30 X 18 X 12 mm (James R., Galena) 



Miscellaneous Remarks: — According to Mr. Marsh this 

 shell bears some resemblance to Unio spatidatus Lea (i. e., U 

 ellipsiformis Conrad), but differs chiefly in being thinner, smaller 

 and more compressed. It is like venusta in that the female shell 

 is deeply emarginate or constricted in front of post-umbonal ridge 

 as the writer determines from the author's description (1891, p. 2). 

 This species was dedicated to Mr. Elwood Pleas of Indiana who 

 collected this Species, together with many other rare Species, 

 from South Missouri. It was also collected by Mr. S. M. Godbey 

 at Morrisville, Polk Co., Missouri, who sent it to the National 

 Museum where it is now recorded under the number, 132634. 

 The writer found pkasii as a rather common shell in the White 

 River, this State. 



Nephronaias ozarkensis (Call). 

 ("The Ozark vShell.") 



{Not figured.) 



1887 — Unio ozarkensis Call, Pr. U. S. Nat. Mus., X, p. 498, pi. XXVII; 

 1895, Tr. Ac. Sci. St. Louis, VII, pp. 33-34, PI- XVIII. 



1900b — Lampsilis ozarkensis Simpson, Pr. U. S. Nat. Mus., XXII, 

 P- .557- 



Animal Characters: — Reference to rough field notes show 



